Tardive Dyskinesia with Antipsychotic Medication in Children and Adolescents: A Systematic Literature Review.

BACKGROUND: Tardive dyskinesia (TD) is a persisting, and potentially irreversible, movement disorder associated with treatment with dopamine receptor antagonists. Few data are available on the risk of TD in children and adolescents treated with antipsychotic medication. OBJECTIVE: To review the literature on incidence, risk factors, and treatment options for antipsychotic-associated TD in children and adolescents (aged < 18 years). METHODS: Relevant articles were identified through a systematic search of Embase and Medline performed in January 2024. Methodological quality was assessed using the Newcastle-Ottawa Scale and Joanna Briggs Institute Critical Appraisal tools. RESULTS: Thirteen studies were identified. The reported TD point prevalence was 5-20%, with higher rates in studies involving typical antipsychotics. Lower estimates (around 1%) emerged from analyses of clinical database data suggesting underdiagnosis in clinical practice. Risk factors included treatment with typical antipsychotics, higher doses, longer duration of exposure, older age, female gender, higher baseline Abnormal Involuntary Movements Scale (AIMS) scores, intellectual impairment, and perinatal complications. CONCLUSION: Although relatively few cases have been reported in children and adolescents, TD remains a risk in this population. Individuals receiving antipsychotics should be monitored carefully for the emergence of abnormal movements. Other than dose reduction, discontinuation, or switch to a lower-risk antipsychotic, few interventions have demonstrated efficacy. The strongest evidence for pharmacological treatment is for VMAT-2 inhibitors (valbenazine and deutetrabenazine), but these drugs are not licensed for use in children. To reduce risk, antipsychotics should be prescribed only if necessary, at the minimum effective dose and for the minimum necessary duration.

Evaluating fenfluramine hydrochloride as an oral solution for the treatment of seizures associated with Lennox-Gastaut syndrome.

INTRODUCTION: Lennox-Gastaut syndrome (LGS) is a severe childhood-onset developmental and epileptic encephalopathy characterized by treatment-refractory seizures, including tonic/atonic 'drop' seizures, and intellectual impairment and slow spike-wave discharges on the electroencephalogram. Fenfluramine, previously prescribed as a weight-loss drug but then withdrawn, has recently been approved in the US, EU, and UK for the adjunct treatment of seizures associated with LGS. AREAS COVERED: The authors review the efficacy and safety findings from clinical trials of fenfluramine in LGS. The authors then discuss the evidence for adverse effects that may be of particular concern to fenfluramine, namely cardiac abnormalities, and weight loss, in the context of the use of fenfluramine for the treatment of the refractory seizures in LGS. EXPERT OPINION: Fenfluramine has demonstrated efficacy in reducing the frequency of seizures in LGS, notably drop seizures, in short-term and long-term clinical trials. Valvular heart disease and pulmonary hypertension have not been reported at the low doses (≤26 mg/day) used in these studies, however, data are limited. Due to its novel mechanism of action, fenfluramine may be of benefit in LGS which has not responded adequately to other antiseizure medications. However, none of these medications, including fenfluramine, achieves the ultimate goal of seizure freedom in most cases.

Culturally compelled coping and depressive symptoms in Black Americans: Examining the role of psychophysiological regulatory capacity.

Given the culture of racism in the United States, Black Americans are often required to use culturally compelled coping (CCC) styles, such as emotional and behavioral restraint and vigilance. Although CCC is adaptive in the face of pervasive racialized stress, it may still negatively impact mental health outcomes, like depression. Studies have found that Black Americans exhibit higher resting heart rate variability (HRV)-a trait-level biomarker of self-regulatory capacity-than White Americans (Hill et al., 2015), which may reflect the additional resources that Black Americans need to regulate given experiences of racialized stress. Theoretically, this should protect against the development of mental health issues, like depression, given that lower resting HRV is typically observed in psychopathology (Beauchaine & Thayer, 2015). However, the literature is mixed on the buffering effects of greater resting HRV on psychopathology for Black Americans (Keen et al., 2015). Thus, we aimed to understand, with data collected from Black Americans between 2015 and 2018, how individual differences in resting HRV and the use of CCC, particularly restraint and vigilance, related to self-reported depressive symptoms. We found that at higher levels of resting HRV, greater use of CCC was associated with higher depressive symptoms. This suggests that CCC strategies may be detrimental to emotional well-being for those who have the capacity-as indexed by higher resting HRV-to engage in these strategies. Hence, the present study provides preliminary evidence that the ways Black Americans are often compelled to cope with racialized stress may be a path to greater depressive symptoms. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Drug-drug interactions between antiseizure medications and antipsychotic medications: a narrative review and expert opinion.

INTRODUCTION: Antiseizure medications (ASMs) and antipsychotic drugs are frequently coadministered with the potential for drug-drug interactions. Interactions may either be pharmacokinetic or pharmacodynamic, resulting in a decrease or increase in efficacy and/or an increase or decrease in adverse effects. AREAS COVERED: The clinical evidence for pharmacokinetic and pharmacodynamic interactions between ASMs and antipsychotics is reviewed based on the results of a literature search in MEDLINE conducted in April 2023. EXPERT OPINION: There is now extensive published evidence for the clinical importance of interactions between ASMs and antipsychotics. Enzyme-inducing ASMs can decrease blood concentrations of many of the antipsychotics. There is also evidence that enzyme-inhibiting ASMs can increase antipsychotic blood concentrations. Similarly, there is limited evidence showing that antipsychotic drugs may affect the blood concentrations of ASMs through pharmacokinetic interactions. There is less available evidence for pharmacodynamic interactions, but these can also be important, as can displacement from protein binding. The lack of published evidence for an interaction should not be interpreted as meaning that the given interaction does not occur; the evidence is building continually. There is no substitute for careful patient monitoring and sound clinical judgment.

Current and emerging pharmacotherapy for the treatment of Lennox-Gastaut syndrome.

INTRODUCTION: Lennox-Gastaut syndrome (LGS) is a severe childhood-onset epileptic encephalopathy, characterized by multiple seizure types, generalized slow spike-and-wave complexes in the EEG, and cognitive impairment. Seizures in LGS are typically resistant to treatment with antiseizure medications (ASMs). Tonic/atonic ('drop') seizures are of particular concern, due to their liability to cause physical injury. AREAS COVERED: We summarize evidence for current and emerging ASMs for the treatment of seizures in LGS. The review focuses on findings from randomized, double-blind, placebo-controlled trials (RDBCTs). For ASMs for which no double-blind trials were identified, lower quality evidence was considered. Novel pharmacological agents currently undergoing investigation for the treatment of LGS are also briefly discussed. EXPERT OPINION: Evidence from RDBCTs supports the use of cannabidiol, clobazam, felbamate, fenfluramine, lamotrigine, rufinamide, and topiramate as adjunct treatments for drop seizures. Percentage decreases in drop seizure frequency ranged from 68.3% with high-dose clobazam to 14.8% with topiramate. Valproate continues to be considered the first-line treatment, despite the absence of RDBCTs specifically in LGS. Most individuals with LGS will require treatment with multiple ASMs. Treatment decisions should be individualized and take into account adverse effects, comorbidities, general quality of life, and drug interactions, as well as individual efficacy.

Current evidence for adjunct pyridoxine (vitamin B6) for the treatment of behavioral adverse effects associated with levetiracetam: A systematic review.

BACKGROUND: Levetiracetam (LVT), while an effective treatment for multiple seizure types, is associated with a high incidence of neuropsychiatric adverse events (NPAEs). In predominantly retrospective studies, supplementation with pyridoxine/vitamin B6 (PN) was associated with improvement in NPAEs in some people. A previous review highlighted a lack of double-blind, controlled trials of PN for the treatment of NPAEs in individuals treated with LVT. The current paper updates the findings from the previous review to include evidence from studies published since June 2019. METHODS: An updated systematic review of the published literature was performed in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed, Embase, the Cochrane Library, and Google Scholar were searched to identify studies published between June 2019 and 2nd November 2022 in which supplementary PN was initiated for the treatment of LVT-associated NPAEs. All study types were eligible. The risk of bias in randomized trials was assessed using the Cochrane risk-of-bias tool. RESULTS: Seven additional studies were identified: two double-blind, randomized controlled trials (RCTs), four retrospective studies, and one retrospective case series. One RCT reported significant improvements from baseline in behavioral adverse events (BAEs) in both the intervention (PN) group and the low-dose control group (both p < 0.05), with a significantly greater improvement in the intervention group (p < 0.001). In the second RCT, differences in BAE severity between PN and placebo groups at the endpoint were not statistically significant. In one retrospective study, subjective irritability was reported to have improved from baseline in 9/20 individuals (45%) treated with supplementary PN. Data for systematic assessments (PHQ-9 and GAD-7) were available for 10 individuals. Assessment by PHQ-9 showed that six individuals improved, two worsened and two had no change. Based on the GAD-7, three people improved, two worsened and five had no change. In the second retrospective study, 18/41 individuals (44%) who commenced PN following the emergence of BAEs showed "significant" improvement. In a separate group of individuals with pre-existing behavioral problems in whom PN treatment was initiated at the same time as commencing LVT, 3/18 (16.7%) developed BAEs. This compared with 79/458 people (17.2%) who were initially treated only with LVT. The third retrospective study compared treatment-related irritability in individuals who had been treated with both LVT and perampanel, either sequentially or concomitantly. Two people who developed irritability while receiving LVT monotherapy were able to continue treatment with the addition of PN. The fourth study reported a significantly lower LVT discontinuation rate in individuals taking PN and a higher rate of improved behavior in those who were able to continue LVT. The case series reported improvements in behavioral symptoms in six people within two to three weeks of commencing supplementary PN. CONCLUSION: Data published within the last three years add to earlier evidence suggesting that PN might be effective in the treatment of NPAEs associated with LVT. However, the quality of evidence remains poor and only a few prospective trials have been published. Data from placebo-controlled trials are still largely lacking. Currently, there is insufficient evidence to justify any firm recommendation for PN supplementation to treat NPAEs associated with LVT. Further well-designed, prospective trials are warranted.

Attention Training as a Low-Intensity Treatment for Concerning Anxiety in Clinic-Referred Youth.

Although youth anxiety treatment research has focused largely on severe and impairing anxiety levels, even milder anxiety levels, including levels that do not meet full criteria for a diagnosis, can be impairing and cause for concern. There is a need to develop and test viable treatments for these concerning anxiety levels to improve functioning and reduce distress. We present findings from a randomized controlled efficacy trial of attention bias modification treatment (ABMT) and attention control training (ACT) for youths with concerning anxiety levels. Fifty-three clinic-referred youths (29 boys, M age = 9.3 years, SD age = 2.6) were randomized to either ABMT or ACT. ABMT and ACT consisted of attention-training trials in a dot-probe task presenting angry and neutral faces; probes appeared in the location of neutral faces in 100% of ABMT trials and 50% of ACT trials. Independent evaluators provided youth anxiety severity ratings; youths and parents provided youth anxiety severity and global impairment ratings; and youths completed measures of attention bias to threat and attention control at pretreatment, posttreatment, and 2-month follow-up. In both arms, anxiety severity and global impairment were significantly reduced at posttreatment and follow-up. At follow-up, anxiety severity and global impairment were significantly lower in ACT compared with ABMT. Attention control, but not attention bias to threat, was significantly improved at follow-up in both arms. Changes in attention control and attention focusing were significantly associated with changes in anxiety severity. Findings support the viability of attention training as a low-intensity treatment for youths with concerning anxiety levels, including levels that do not meet full criteria for a diagnosis. Superior anxiety reduction effects in ACT highlight the critical need for mechanistic research on attention training in this population.

Should Antidepressants be Avoided in Pregnancy?

Many (> 40%) women discontinue antidepressants during pregnancy because of concerns about effects on the foetus, based on information from inadequately-controlled studies. The sibling-control study design provides the best control for confounding factors, notably maternal depression. The purpose of this review was to investigate the evidence from sibling-control analyses for adverse outcomes in offspring associated with antidepressant exposure during pregnancy. Fourteen sibling-control studies were identified through searches of PubMed and Embase. Outcomes included preterm birth, small for gestational age, neonatal size, birth defects, autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), behavioural problems, neurodevelopmental deficits, and scholastic attainment. For the majority of these outcomes, no statistically significant associations were found when comparing exposed and unexposed siblings. Single studies reported associations with preterm birth, reduced gestational age, ADHD, anxiety at 36 months, and lower mathematics test scores, which persisted in the sibling-control analyses. However, differences were small and possibly not clinically significant. Moreover, effects of residual confounding could not be excluded. These findings provide evidence that many of the previously reported associations between prenatal antidepressant exposure and adverse outcomes in offspring are no longer statistically significant when exposed offspring are compared with unexposed siblings. The few statistically significant differences in sibling-control analyses were generally small with doubtful clinical significance. Decisions on antidepressant treatment during pregnancy should be made individually, based on evidence from properly controlled studies, not on misleading information based on studies that have not controlled adequately for confounding factors.

Adverse events in long-term studies of exogenous melatonin.

INTRODUCTION: Exogenous melatonin is regulated as a drug in the UK and EU but is available as an over-the-counter dietary supplement in the US and Canada. In the last 15 years, melatonin use has increased rapidly in many countries, in particular, in children and adolescents who frequently have many years of continuous exposure. Despite this, the potential risks associated with extended use continue to be unclear, and there remains a lack of systematically assessed safety data from long-term prospective trials. AREAS COVERED: This review focuses on adverse event data reported in long-term (≥6 months) prospective trials of melatonin. METHODS: The Embase and Medline electronic databases were searched from inception to 12 September 2022 for long-term studies of melatonin, in which adverse events were systematically monitored and reported. EXPERT OPINION: Although the reported frequency of possible adverse events associated with long-term melatonin use is low and few clinically significant adverse events have been reported, the scarcity of data from double-blind randomized placebo-controlled trials should caution against complacency. Ideally, analysis of data from large well-established research databases should be conducted to provide good quality evidence on which to base a more rigorous evaluation of the safety profile.

Evaluating interactions between emotion regulation strategies through the interpersonal context of female friends.

INTRODUCTION: There is a growing interest in examining how interpersonal relationships may shape associations between emotion regulation (ER) strategies and psychopathology. METHODS: We used multilevel modeling to test if respondents' self-reported intrapersonal ER, friends' self-reported intrapersonal ER, and their interaction were associated with psychopathology in a sample of 120 female friend dyads. RESULTS: Respondents' use of brooding rumination, expressive suppression, and worry were positively associated with respondent psychopathology. Friend reappraisal moderated the association between respondent reappraisal and respondent psychopathology. Consistent with an interference hypothesis, respondent cognitive reappraisal was only associated with respondent psychopathology when friend cognitive reappraisal was low. Consistent with a compensatory hypothesis, respondent reappraisal was primarily associated with respondent psychopathology when friend repetitive negative thought was high. DISCUSSION: Results support the extension of models of ER strategy interactions from intrapersonal to interpersonal contexts. Future research is needed to replicate the interference and compensatory interactions observed in the data.

Efficacy and safety of lamotrigine in the treatment of bipolar disorder across the lifespan: a systematic review.

BACKGROUND: Bipolar disorder (BD) is a cyclic mood disorder characterised by alternating episodes of mania/hypomania and depression interspersed with euthymic periods. Lamotrigine (LTG) demonstrated some mood improvement in patients treated for epilepsy, leading to clinical studies in patients with BD and its eventual introduction as maintenance therapy for the prevention of depressive relapse in euthymic patients. Most current clinical guidelines include LTG as a recommended treatment option for the maintenance phase in adult BD, consistent with its global licencing status. AIMS: To review the evidence for the efficacy and safety of LTG in the treatment of all phases of BD. METHODS: PubMed was searched for double-blind, randomised, placebo-controlled trials using the keywords: LTG, Lamictal, 'bipolar disorder', 'bipolar affective disorder', 'bipolar I', 'bipolar II', cyclothymia, mania, manic, depression, depressive, 'randomised controlled trial', 'randomised trial', RCT and 'placebo-controlled' and corresponding MeSH terms. Eligible articles published in English were reviewed. RESULTS: Thirteen studies were identified. The strongest evidence supports utility in the prevention of recurrence and relapse, particularly depressive relapse, in stabilised patients. Some evidence suggests efficacy in acute bipolar depression, but findings are inconsistent. There is little or no strong evidence in support of efficacy in acute mania, unipolar depression, or rapid-cycling BD. Few controlled trials have evaluated LTG in bipolar II or in paediatric patients. Indications for safety, tolerability and patient acceptability are relatively favourable, provided there is slow dose escalation to reduce the probability of skin rash. CONCLUSION: On the balance of efficacy and tolerability, LTG might be considered a first-line drug for BD, except for acute manic episodes or where rapid symptom control is required. In terms of efficacy alone, however, the evidence favours other medications.

Pharmacological treatment for Tourette syndrome in children and adults: What is the quality of the evidence? A systematic review.

BACKGROUND: Tourette syndrome (TS) is a neurodevelopmental disorder characterised by involuntary muscle movements manifesting as motor and vocal tics. In the majority, tics are manageable without medication. Where tics cause discomfort or impair function, behavioural or pharmaceutical treatments may be considered. AIMS: To provide a meticulous examination of the quality of evidence for the current pharmacological treatments for TS. METHODS: PubMed and Google Scholar were searched to identify randomised, placebo-controlled trials (RCTs) of aripiprazole, risperidone, clonidine, guanfacine, haloperidol, pimozide, tiapride and sulpiride for the treatment of tics in children and adults with TS. Quality of reporting and risk of bias were assessed against the CONSORT checklist and Cochrane risk of bias criteria, respectively. RESULTS: Seventeen RCTs were identified. Response rates reached 88.6% for aripiprazole, 68.9% for clonidine, 62.5% for risperidone and 19% for guanfacine. Statistically significant improvements were reported for all medications compared to placebo in at least one study and for at least one measure of tic severity. Most studies predated the CONSORT and Cochrane criteria and did not score highly when assessed on these measures. CONCLUSIONS: There are relatively few placebo-controlled trials of commonly prescribed medications. Studies are often of poor quality and short duration. There is evidence for the efficacy of each medication, but no drug is clearly superior. Clonidine and guanfacine are better tolerated than antipsychotics, but less effective. There is too little evidence to determine whether adults respond differently from children.

Gender Matters: Nonlinear Relationships Between Heart Rate Variability and Depression and Positive Affect.

Vagally mediated heart rate variability (vmHRV), a measure of the parasympathetic nervous system's control over the heart, is often negatively related to maladaptive emotional outcomes. Recent work suggests that quadratic relationships involving these factors may be present; however, research has not investigated gender differences in these nonlinear functions. To address this gap, the current study tested for quadratic relationships between resting vmHRV and depression and positive affect while investigating gender differences in these relationships. Significant quadratic effects were found between resting vmHRV and reports of both depression symptoms and positive affect in women but not men. Specifically, the lowest levels of depression and the highest levels of positive affect were found at moderate vmHRV in women. These results suggest that examinations of vmHRV's nonlinear associations require the consideration of gender. Our findings are interpreted based on proposed differential neuropsychological mechanisms of vmHRV in men versus women.

Neurocognitive Effects of Antiseizure Medications in Children and Adolescents with Epilepsy.

Impairments in cognition are common in epilepsy and may be caused or exacerbated by antiseizure medications (ASMs). Positive effects on cognition may also be seen with some ASMs. Cognitive outcomes are of particular concern in children who may be at an increased risk of cognitive adverse effects of treatment. A comprehensive literature search was conducted in PubMed in order to evaluate the evidence for cognitive changes associated with treatment with ASMs in paediatric epilepsy patients. The ASMs considered were those in the current edition of the British National Formulary (BNF). For most ASMs, remarkably few studies providing robust data on cognitive effects in paediatric patients were identified. The available evidence suggests cognitive impairments may be associated with treatment with phenobarbital. Topiramate and phenytoin are also associated with negative effects on cognition, in particular word-finding difficulties and other language deficits with topiramate, but there are few data available specifically on children. Lamotrigine, levetiracetam and fenfluramine are associated with improvements in some cognitive domains, although it is unclear whether these effects are directly attributable to the medications or are a result of improvements in seizures. Neutral effects on cognition (no substantial evidence of worsening) were suggested for carbamazepine, everolimus, lacosamide, oxcarbazepine, perampanel and valproate. There is limited data for cannabidiol, clobazam, eslicarbazepine acetate, ethosuximide, rufinamide, vigabatrin and zonisamide, although the available evidence suggests these drugs are not associated with severe cognitive impairment. There was too little information to reach conclusions about the effects of brivaracetam, felbamate, gabapentin, pregabalin, retigabine, stiripentol or tiagabine.

Is Adjunct Aripiprazole Effective in Treating Hyperprolactinemia Induced by Psychotropic Medication? A Narrative Review.

Psychotropic medication treatment can cause elevated serum prolactin levels and hyperprolactinaemia (HPRL). Reports have suggested that aripiprazole may decrease elevated prolactin. The aim of this review was to assess evidence for the efficacy of adjunct aripiprazole in the treatment of psychotropic-induced HPRL. PubMed and Google Scholar were searched to identify randomised placebo-controlled trials (RCTs) of adjunct aripiprazole in patients with HPRL attributed to primary psychotropic medications. Data for individual patients from case studies, chart reviews and open-label studies were also identified and assessed. Six RCTs, with a total of 609 patients, met inclusion criteria. Primary psychotropics included risperidone, haloperidol, paliperidone, fluphenazine and loxapine. Reductions in prolactin from baseline, before the introduction of aripiprazole, were significantly greater for adjunct aripiprazole than for adjunct placebo in all the studies (p = 0.04 to p < 0.0001). Normalisation of serum prolactin levels was significantly more likely with adjunct aripiprazole than adjunct placebo (p = 0.028 to p < 0.001, data from three studies). Improvement or resolution of HPRL-related symptoms (galactorrhoea, oligomenorrhoea, amenorrhoea and sexual dysfunction) were reported in three studies. Prolactin levels decreased in all case reports and in both of two open-label studies; they normalised in 30/41 patients (73.2%) in case studies and 12/29 (41.4%) in the open-label studies. Adjunct aripiprazole was statistically significantly effective in treating elevated serum prolactin levels in six RCTs. Evidence from case reports and open-label studies suggests a degree of effectiveness in most patients.

Seizures and Epilepsy in Autism Spectrum Disorder.

Epilepsy and autism frequently co-occur. Epilepsy confers an increased risk of autism and autism confers an increased risk of epilepsy. Specific epilepsy syndromes, intellectual disability, and female gender present a particular risk of autism in individuals with epilepsy. Epilepsy and autism are likely to share common etiologies, which predispose individuals to either or both conditions. Genetic factors, metabolic disorders, mitochondrial disorders, and immune dysfunction all can be implicated.

Social anxiety symptoms, heart rate variability, and vocal emotion recognition in women: evidence for parasympathetically-mediated positivity bias.

BACKGROUND AND OBJECTIVES: Individuals with social anxiety disorder show pronounced perceptual biases in social contexts, such as being hypervigilant to threat and discounting positive social cues. Parasympathetic activity influences responses to the social environment and may underlie these biases. This study examined the associations among social anxiety symptoms, heart rate variability (HRV), and vocal emotion recognition. DESIGN AND METHOD: Female undergraduate students (N = 124) self-reported their social anxiety symptoms using the Social Anxiety Disorder Dimensional Scale and completed a computerized vocal emotion recognition task using stimuli from the Ryerson Audio-Visual Database of Emotional Speech and Song stimulus set. HRV was measured at baseline and during the emotion recognition task. RESULTS: Women with more social anxiety symptoms had higher emotion recognition accuracy (p = .021) and rated positive stimuli as less intense (p = .032). Additionally, although those with greater social anxiety symptoms did not have lower resting HRV (p = .459), they did have lower task HRV (p = .026), which mediated their lower positivity bias and greater recognition accuracy. CONCLUSIONS: A parasympathetically-mediated positivity bias may indicate or facilitate normal social functioning in women. Additionally, HRV during a symptom- or disorder-relevant task may predict task performance and reveal parasympathetic differences that are not found at baseline.

Allopatry, hybridization, and reproductive isolation in Arctostaphylos.

PREMISE: Hybridization plays a key role in introgressive adaptation, speciation, and adaptive radiation as a source of evolutionary innovation. Hybridization is considered common in Arctostaphylos, yet species boundaries are retained in stands containing multiple species. Arctostaphylos contains diploids and tetraploids, and recent phylogenies indicate two clades; we hypothesize combinations of these traits limit or promote hybridization rates. METHODS: We statistically analyzed co-occurrence patterns of species by clade membership and ploidy level from 87 random 0.1 ha plots. We sampled multiple sites to analyze for percent hybridization based on morphology. Finally, phenophases were analyzed by scoring herbarium sheets for a large number of taxa from both clades as well as tetraploids, and second, surveying three field sites over two years for divergence in phenological stages between co-occurring taxa. RESULTS: Most taxa in Arctostaphylos are allopatric relative to other congenerics. When two taxa co-occur, the patterns are a diploid with a tetraploid, or two diploids from different clades. When three taxa co-occur, the pattern is two diploids from different clades and a tetraploid. Field and herbarium data both indicate flowering phenology is displaced between diploids from the two clades; one of the diploid clades and tetraploids overlap considerably. CONCLUSIONS: The two deep clades in Arctostaphylos are genetically distant, with hybrids rare or non-existent when taxa co-occur. Reproductive isolation between clades is enhanced by displaced flowering phenology for co-occurring species. Within clades, taxa appear to have few reproductive barriers other than an allopatric distribution or different ploidy levels.