The effect of dopamine partial agonists on the nicotine dependency in patients with schizophrenia

Place of the partial dopamine receptor agonist aripiprazole in the management of schizophrenia in adults: a Delphi consensus study

BACKGROUND

Aripiprazole is a second-generation antipsychotic, efficacious in patients with schizophrenia during acute episodes. Due to its pharmacological profile, aripiprazole may be of interest in patients with specific clinical profiles who have not been studied extensively in randomised clinical trials.

OBJECTIVES

To capture experience with aripiprazole in everyday psychiatric practice using the Delphi method in order to inform decision-making on the use of aripiprazole for the treatment of patients with schizophrenia in clinical situations where robust evidence from clinical trials is lacking.

METHODS

The scope of the survey was defined as the management of schizophrenia in adults. A systematic literature review was performed to identify the different clinical situations in which aripiprazole has been studied, and to describe the level of clinical evidence. Clinical profiles to include in the Delphi survey were selected if there was a clear interest in terms of medical need but uncertainty over the efficacy of aripiprazole. For each clinical profile retained, five to seven specific statements were generated and included in a questionnaire. The final 41-item questionnaire was proposed to a panel of 406 French psychiatrists with experience in the treatment of schizophrenia. Panellists rated their level of agreement using a Likert scale. A second round of voting on eleven items was organised to clarify points for which a consensus was not obtained in the first round.

RESULTS

Five clinical profiles were identified in the literature review (persistent negative symptoms, pregnancy, cognitive dysfunction, addictive comorbidity and clozapine resistance). Sixty-two psychiatrists participated in the first round of the Delphi survey and 33 in the second round. A consensus was obtained for 11 out of 41 items in the first round and for 9/11 items in the second round. According to the panellists' clinical experience, aripiprazole can be used as maintenance treatment for pregnant women, is relevant to preserve cognitive function and can be considered an option in patients with a comorbid addictive disorder or with persistent negative symptoms.

CONCLUSION

These findings may help physicians in choosing relevant ways to use aripiprazole and highlight areas where more research is needed to widen the evidence base.

The Benefits of Olanzapine in Palliating Symptoms

OPINION STATEMENT

Olanzapine has become a major drug in the management of chemotherapy-induced nausea and vomiting as a prophylactic agent. In addition, a recent randomized trial has demonstrated its benefits in treating nausea and vomiting associated with advanced cancer. The added benefit to olanzapine is that it also stimulates appetite. As a result, since it treats multiple symptoms associated with advanced cancer, it is likely to become the antiemetic of choice in palliative care at least in the USA. The added benefit of treating insomnia and the avoidance of benzodiazepines should place olanzapine in at the top of the list of drugs to use for patients who do complain of insomnia. There is no good evidence that it potentiates the respiratory depression of opioids unlike benzodiazepines. The evidence is weak that olanzapine in as an adjuvant analgesic. Hopefully, future trials will explore this in greater depth. The benefits of adding olanzapine to potent opioids are that it may reduce craving, drug cues, and opioid misuse. Other symptoms like anxiety and depression may be addressed by the addition of olanzapine to standard antidepressants.

Potent Dopamine D2 Antagonists Block the Reward-Enhancing Effects of Nicotine in Smokers With Schizophrenia

Antipsychotics that are potent dopamine (DA) D2 receptor antagonists have been linked to elevated levels of nicotine dependence in smokers with schizophrenia. Because activation of D2 receptors mediates motivation for nicotine, we examined whether potent D2 antagonists would diminish nicotine's ability to stimulate reward processing-a mechanism that may drive compensatory increases in smoking. Smokers with schizophrenia (n = 184) were recruited and stratified into medication groups based on D2 receptor antagonist potency. The effects of smoking on reward function were assessed using a probabilistic reward task (PRT), administered pre- and post-smoking. The PRT used an asymmetrical reinforcement schedule to produce a behavioral response bias, previously found to increase under conditions (including smoking) that enhance mesolimbic DA signaling. Among the 98 participants with valid PRT data and pharmacotherapy that could be stratified into D2 receptor antagonism potency, a medication × smoking × block interaction emerged (P = .005). Post-hoc tests revealed a smoking × block interaction only for those not taking potent D2 antagonists (P = .007). This group exhibited smoking-related increases in response bias (P < .001) that were absent in those taking potent D2 antagonists (P > .05). Our findings suggest that potent D2 antagonists diminish the reward-enhancing effects of nicotine in smokers with schizophrenia. This may be a mechanism implicated in the increased rate of smoking often observed in patients prescribed these medications. These findings have important clinical implications for the treatment of nicotine dependence in schizophrenia.

Comparing the effect of clozapine and risperidone on cue reactivity in male patients with schizophrenia and a cannabis use disorder: A randomized fMRI study

OBJECTIVE

Cannabis use disorders (CUDs) are highly comorbid in patients with schizophrenia and associated with poor outcome. Clozapine has been put forward as the first choice antipsychotic in this patient group. However, little is known about the mechanisms underlying the assumed superiority of clozapine.

METHODS

A total of 38 patients with DSM-IV schizophrenia (30 with and 8 without a DSM-IV CUD) and 20 healthy comparison subjects were included between April 2009 and June 2012. Patients were randomized to antipsychotic treatment with clozapine or risperidone. At baseline and after 4weeks of medication, brain response to cannabis-related, positive and neutral images was measured using functional MRI. Neural correlates of cue reactivity were assessed in the following regions of interest: amygdala, ventral striatum, insula, thalamus, orbitofrontal cortex and anterior cingulate cortex. Subjective craving was assessed using self-report questionnaires (OCDUS and MCQ).

RESULTS

At baseline, patients with a comorbid CUD showed higher subjective craving and greater activation in response to cannabis-related images compared to patients without a CUD and healthy controls in most regions of interest. Clozapine treated patients reported a greater reduction in craving (F(1,28)=6.0, p=0.04) and showed a larger decrease in amygdala activation during cannabis-related images compared to risperidone treated patients (T=3.94, pFWE=0.006). In addition, significant correlations were found between subjective craving and thalamus and insula activation during cannabis-related images.

CONCLUSION

These findings provide evidence that clozapine is superior to risperidone in decreasing subjective craving and cue reactivity for cannabis-related images probably due to a differential effect on dopaminergic neurotransmission.

TRIAL REGISTRATION

'Nederlands trial register' (http://www.trialregister.nl), nr NTR1761, http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=1761.

Cigarette smoking and schizophrenia: a specific clinical and therapeutic profile? Results from the FACE-Schizophrenia cohort

BACKGROUND

Tobacco use is common in patients with schizophrenia (SZ) but little is known on the role of tobacco in the physiopathology or on the course of the disease. Only few studies embrace an extensive examination of clinical and therapeutic characteristics in stabilized patients. The objective of the present study was to determine the prevalence of tobacco smoking in stabilized SZ outpatients and the clinical and treatment characteristics associated with daily tobacco use in a large community-dwelling sample of patients.

METHODS

Three-hundred-and-sixty-one patients were included in the network of the FondaMental Expert Centers for Schizophrenia. Current tobacco status was self-declared.

RESULTS

53.7% were smokers. Mean age at tobacco onset was 17.2years old. In multivariate analyses, after adjustment for confounding factors, positive symptoms and mean daily antipsychotic dose were associated with a higher frequency of tobacco use (OR=1.06 95%IC[1.02-1.12], for positive symptoms, OR=1.1, 95%IC[1.02-1.18] for daily antipsychotic dose). Education level, negative symptoms, anticholinergic agents, clozapine or aripiprazole administration were independently associated with a lower frequency of tobacco use (respectively OR=0.87, 95%IC [0.79, 0.95], OR=0.95, 95%IC[0.91-0.98], OR=0.41, 95%IC[0.22-0.76], OR=0.56, 95%IC=[0.32, 0.99] and OR=0.49, 95%IC [0.26-0.91]).

CONCLUSION

The prevalence of current tobacco smoking in a French community-dwelling SZ patients is higher that observed in the general population. Patients with tobacco use present clinical and therapeutic specificities that may involve interaction between cholinergic-nicotinic and dopaminergic systems. The present study suggests that some therapeutics may improve daily smoking behavior in smokers. These results should be confirmed in longitudinal studies.

Medications between psychiatric and addictive disorders

INTRODUCTION

Many epidemiological studies have revealed a frequent co-occurrence of psychiatric and substance use disorders. The term used in the literature to refer to this co-occurrence is dual diagnosis. The high prevalence of dual diagnosis has led physicians to observe the effects of medication prescribed to treat psychiatric disorders on the co-occurring substance use disorder and vice versa. The concept of medications between psychiatric and addictive disorders stems from these clinical observations, alongside which, however, it has developed from the observation that both psychiatric and substance use disorders share common neurobiological pathways and trigger common cognitive disorders. This has led researchers to develop medications on the basis of neurobiological and cognitive rationales.

MATERIAL AND METHOD

In our article, we review peculiar medications based on neurobiological and cognitive rationales and that have an impact in both psychiatric and addictive disorders.

RESULTS

We highlight how interesting these new prescriptions are for clinical observation and for the treatment of patients suffering from dual diagnosis.

CONCLUSION

We then go on to discuss the interest in them from the perspective of clinical practice and clinical research, in that the development of medications to treat dual diagnosis helps to further our knowledge of both psychiatric and substance use disorders.

Systematic Literature Review of the Methods Used to Compare Newer Second-Generation Agents for the Management of Schizophrenia: A focus on Health Technology Assessment

BACKGROUND

The challenges of comparative effectiveness to support health technology assessment (HTA) agencies are important considerations in the choices of antipsychotic medications for the treatment of schizophrenia.

OBJECTIVES

Our aim was to assess the study methods used and outcomes reported in the published literature to address the question of comparative effectiveness of newer antipsychotic agents and the adequacy and availability of evidence to support HTA agencies.

DATA SOURCE

A systematic search of the PubMed database from 1 January 2009 to 30 September 2013 was conducted to identify studies evaluating new atypical antipsychotics reporting on comparative effectiveness.

STUDY SELECTION

The systematic review comprised of studies on schizophrenia patients where at least two drugs were being compared and at least one treatment group received one of the following second-generation antipsychotics: risperidone, olanzapine, aripiprazole, paliperidone, asenapine, iloperidone, lurasidone, and quetiapine. The included studies were also required to have an efficacy, safety or economic outcome, such as Positive and Negative Syndrome Scale (PANSS) score, weight gain, resource utilization, or costs.

STUDY APPRAISAL AND SYNTHESIS METHODS

Two reviewers (BW and GK) independently applied the inclusion criteria. Disagreements between reviewers were resolved by consensus, referring to the original sources. Information on the methodology and outcomes was collected for each included study. This included study description, head-to-head drug comparison, patient population, study methodology, statistical methods, reported outcomes, study support, and journal type.

RESULTS

A total of 198 studies were identified from electronic search methods. The largest category of studies was randomized controlled trials [RCTs] (N = 73; 36.9%), which were largely directed at the regulatory endpoint. Fewer studies were undertaken for HTA-purposes cohort studies (N = 53; 26.8%), meta-analyses (N = 32; 16.2%), economic studies (N = 14; 7.1%), and cross-sectional studies (N = 13; 6.6%). Direct head-to-head comparisons preferred by HTA were dominated by the comparison involving olanzapine and risperidone, representing 149 (75.3%) and 119 (60.1%) studies, respectively. RCTs, which are the primary study type for regulatory submissions, showed a lack of bias. Studies aimed at HTA were not as well performed. Cohort studies suffered from bias in the selection of comparison groups, lack of control for confounders, and differential dropout rates. As a group, cross-sectional studies scored poorly for bias, with a primary failure to identify a representative sample. Economic studies showed highly variable bias, with bias in the representation of effectiveness data, model assumptions without validation, and lack of sensitivity analyses.

LIMITATIONS

One limitation of this systematic review is that it only included studies from 2009 to 2013, potentially excluding some earlier comparator studies, particularly those involving first-generation antipsychotics.

CONCLUSIONS

This review of comparative effectiveness studies of second-generation antipsychotic agents for schizophrenic patients revealed a wide range of study types, study methodologies, and outcomes. For traditional efficacy outcomes and select safety outcomes, there is strong evidence from many well-conducted studies; however, there are fewer studies of types preferred by HTA with limited head-to-head comparisons and a higher risk of bias in the execution of these studies.

Advances in nicotine research in Addiction Biology

The aim of Addiction Biology is to advance our understanding of the action of drugs of abuse and addictive processes via the publication of high-impact clinical and pre-clinical findings resulting from behavioral, molecular, genetic, biochemical, neurobiological and pharmacological research. As of 2013, Addiction Biology is ranked number 1 in the category of Substance Abuse journals (SCI). Occasionally, Addiction Biology likes to highlight via review important findings focused on a particular topic and recently published in the journal. The current review summarizes a number of key publications from Addiction Biology that have contributed to the current knowledge of nicotine research, comprising a wide spectrum of approaches, both clinical and pre-clinical, at the cellular, molecular, systems and behavioral levels. A number of findings from human studies have identified, using imaging techniques, alterations in common brain circuits, as well as morphological and network activity changes, associated with tobacco use. Furthermore, both clinical and pre-clinical studies have characterized a number of mechanistic targets critical to understanding the effects of nicotine and tobacco addiction. Together, these findings will undoubtedly drive future studies examining the dramatic impact of tobacco use and the development of treatments to counter nicotine dependence.

Pharmacotherapy of Co-Occurring Schizophrenia and Substance Use Disorders

Substance use disorders, common in patients with schizophrenia, can lead to poor outcomes. Here we review the literature on the use of antipsychotics in patients with co-occurring schizophrenia and substance use disorder as well as evidence for the use of adjunctive pharmacological treatments targeting substance use in these patients. We also discuss a neurobiological formulation suggesting that the cooccurrence of these disorders may be related to a dysfunction in the dopamine mediated brain reward circuitry. Typical antipsychotics do not appear to decrease substance use in this population. Randomized, controlled trials provide some support for use of the atypical antipsychotic clozapine for co-occurring cannabis use disorder, naltrexone and disulfiram for alcohol use disorder, and also nicotine replacement therapy, sustained-release bupropion and varenicline for tobacco use disorder. Nonetheless, data regarding treatment in patients with these co-occurring disorders are still limited, and many studies reported to date have been either underpowered or did not include a control condition. Further research is needed to evaluate optimal pharmacotherapeutic strategies for this population.

Allostatic load as a tool for monitoring physiological dysregulations and comorbidities in patients with severe mental illnesses

Severe mental illnesses like schizophrenia and bipolar disorder are disabling, chronic conditions that are often accompanied by medical comorbidities. In this theoretical article, we review the allostatic load model representing the "wear and tear" that chronic stress exacts on the brain and body. We propose an innovative way of monitoring physical and psychiatric comorbidities by integrating the allostatic load model into clinical practice. By interpreting peripheral biomarkers differently, medical professionals can calculate a simple, count-based, allostatic load index known to predict diverse stress-related pathologies. In addition to screening for comorbidities, allostatic load indices can be used to monitor the effects of pharmacological and psychosocial interventions. This framework can also be used to generate a dialogue between patient and practitioner to promote preventive and proactive approaches to health care.

Do atypical antipsychotics really enhance smoking reduction more than typical ones?: the effects of antipsychotics on smoking reduction in patients with schizophrenia

Whether atypical antipsychotics (AAs) can enhance smoking reduction in schizophrenic patients remains controversial because of methodological limitations in existing studies. This study explored whether certain types of antipsychotics predict smoking reduction in schizophrenic patients. Three hundred eight smoking, predominantly male schizophrenic patients (271/308 [88.9%]) participated in an 8-week open-label study with antismoking medications (high-dose, low-dose nicotine transdermal patch and bupropion). Antipsychotics were classified into (1) typical antipsychotics (TAs) and (2) AAs, including multiacting receptor-targeted antipsychotics (clozapine, olanzapine, and quetiapine), serotonin-dopamine antagonists (risperidone), D2/D3 receptor antagonists (amisulpride), and partial dopamine receptor agonists (aripiprazole). A general linear model was used to explore whether types of antipsychotic predict changes in the number of cigarettes smoked per day (CPD) and the score of the Fagerstrom Test for Nicotine Dependence (FTND) while controlling for confounding factors. The type of antipsychotic (TAs or AAs) was not significantly associated with smoking cessation (n = 21; χ = 1.8; df = 4; P = 0.77). Regarding smoking reduction, the type of antipsychotic was significantly predictive of a change in the CPD (P = 0.027; partial eta square = 0.055) and FTND scores (P = 0.002; partial eta square = 0.073). The 95% confidence intervals of the estimated means of change in the CPD and FTND scores did not contain zero only among subjects on TAs or clozapine.These findings suggest that TAs and clozapine enhance smoking reduction compared with nonclozapine atypical antipsychotics in schizophrenic patients. The mechanisms underlying the effects of various antipsychotics on smoking reduction remain unclear and warrant future study.

Effectiveness of aripiprazole in the treatment of adult Tourette patients up to 56 months

OBJECTIVE

Tourette Syndrome (TS) is characterized by motor and vocal tics. Its pharmacological treatment is often a challenge because of the so-called tachyphylactic effects. Aripiprazole has been reported to be effective in small case series with short follow-up periods.

METHODS

In a retrospective analysis, we assessed the effect of off-label treatments with aripiprazole in 20 adult patients (mean age 27.4) divided in a group of severely [67 Yale Global Tourette Severity Scale (YGTTS)-total] and moderately (43.3 YGTTS-total) affected patients. TS patients were treated with aripiprazole (mean 11.8 mg daily) and followed for up to 56 months.

RESULTS

Applying a random coefficient model, we found a significant benefit resulting from treatment with aripiprazole. This effect was larger in the severely affected patient group in comparison with the moderately affected patient group. The effect was stable over a time period up to 56 months.

CONCLUSION

Aripiprazole, a neuroleptic drug of the third generation with a partial D(2) -agonism is effective in moderately and severely affected adult Tourette patients. We add to the current knowledge through our data extending the follow-up interval up to a maximum of 56 months. All available clinical data strongly support the initiation of a double-blind placebo or other neuroleptic substance controlled trial.

Treatment of dual diagnosis disorders

PURPOSE OF REVIEW

Treatment of dual diagnosis [co-occurrence of a substance use disorder (SUD) in patients with mental illness] poses several challenges for mental health professionals. This article seeks to review the recent advances in dual diagnosis treatment with respect to pharmacotherapy and psychosocial approaches.

RECENT FINDINGS

Atypical antipsychotics are commonly used for comorbid schizophrenia and SUD. Whereas there is no difference between risperidone and olanzapine, clozapine appears to have a distinct advantage in reducing psychotic symptoms as well as substance abuse (including smoking). There is emerging evidence that quetiapine is beneficial in dually diagnosed patients, particularly using alcohol, cocaine and amphetamine. A combination of naltrexone and sertraline was found to be effective in patients with depressive disorder and alcohol dependence. Effectiveness of atomoxetine is yet to be established in patients with comorbid adult attention-deficit/hyperactivity disorder with respect to decrease in substance abuse. Integrated intervention is the choice of treatment for patients with dual diagnosis.

SUMMARY

In spite of the high association between substance use and psychiatric disorders, there is a surprising paucity of studies related to treatment and outcome. A few well-designed studies have been recently published and more studies of this nature are required in order to address the challenges posed in the treatment of dual disorders.

South Korean military service promotes smoking: a quasi-experimental design

PURPOSE

The South Korean (SK) government monopolizes the tobacco industry and is accused of pushing smoking on captive military personnel. However, estimating the association between military service and smoking is difficult, since military service is required for all SK men and the few civilian waivers are usually based on smoking determinants, e.g., social status.

MATERIALS AND METHODS

Using a quasi-experimental design we validly estimate the association between military service and smoking. Military service was assigned by immigration patterns to the United States, instead of an experimenter, by comparing Korean Americans who happened to immigrate before or after the age(s) of mandated service. Smoking promotion in the military was also described among SK veterans, to identify the probable mechanisms for veterans' smoking tendencies.

RESULTS

Veterans were 15% [95% confidence interval (CI), 4 to 27] more likely to ever-puff and 10% (95% CI, 0 to 23) more likely to ever-smoke cigarettes, compared to a similar group of civilians. Among veterans, 92% (95% CI, 89 to 95) recalled cigarettes were free, 30% (95% CI, 25 to 35) recalled smokers were given more work breaks and 38% (95% CI, 32 to 43) felt explicit "social pressure" to smoke. Free cigarettes was the strongest mechanism for veterans' smoking tendencies, e.g., veterans recalling free cigarette distribution were 16% (95% CI, 1 to 37) more likely to ever-smoke than veterans not recalling.

CONCLUSION

These patterns suggest military service is strongly associated with smoking, and differences between veterans and civilians smoking may carry over long after military service. Given military service remains entirely in government purview, actively changing military smoking policies may prove most efficacious. This highlights the importance of recent bans on military cigarette distribution, but policies eliminating other smoking encouragements described by veterans are necessary and could effectively reduce the smoking prevalence by as much as 10% in SK.

Differences in craving for cannabis between schizophrenia patients using risperidone, olanzapine or clozapine

Substance abuse and psychotic disorders have a high rate of comorbidity. Both disorders are associated with changes in the dopaminergic transmission in the mesocorticolimbic pathways of the brain. Since antipsychotic medications interact with the dopamine receptors in these pathways, these medications could affect craving for substances. In the current study, the effect of clozapine (n = 27, mean dosage 350 mg), risperidone (n = 54, mean dosage 3.46 mg) and olanzapine (n = 60, mean dosage 13.78 mg) on subjective craving for cannabis was compared in 123 patients with cannabis dependence and psychotic disorder. Patients treated with risperidone reported significantly more craving compared with patients treated with clozapine (Z = -3.19, p = .001) or olanzapine (Z = -2.24, p = .025). No significant differences in craving between clozapine and olanzapine were found. These results are in concordance with findings in the literature on this subject and could be explained by differences in three dopamine mediated mechanisms of these compounds: 1) occupancy rate of dopamine D(2) receptors, 2) dissociation rate of dopamine D(2) receptors, 3) D(1)/D(2) occupancy ratio. Risperidone and clozapine show a maximal difference in D(2) receptor occupancy rate, dissociation rate and D(1)/D(2) ratio. Olanzapine is intermediate between risperidone and clozapine in these characteristics.

A transdisciplinary perspective of chronic stress in relation to psychopathology throughout life span development

The allostatic load (AL) model represents an interdisciplinary approach to comprehensively conceptualize and quantify chronic stress in relation to pathologies throughout the life cycle. This article first reviews the AL model, followed by interactions among early adversity, genetics, environmental toxins, as well as distinctions among sex, gender, and sex hormones as integral antecedents of AL. We next explore perspectives on severe mental illness, dementia, and caregiving as unique human models of AL that merit future investigations in the field of developmental psychopathology. A complimenting transdisciplinary perspective is applied throughout, whereby we argue that the AL model goes beyond traditional stress–disease theories toward the advancement of person-centered research and practice that promote not only physical health but also mental health.

The role of antipsychotics in smoking and smoking cessation

Persons with severe and persistent mental illnesses, e.g. schizophrenia spectrum disorders and bipolar disorder, smoke at a much higher rate than the general population. Treatment options for schizophrenia spectrum disorders and bipolar disorder often include the first-generation (typical) and second-generation (atypical) antipsychotics, which have been shown to be effective in treating both psychotic and mood symptoms. This article reviews studies examining the relationship between antipsychotic medication and cigarette smoking. These studies suggest that in persons with schizophrenia and schizoaffective disorder, typical antipsychotics may increase basal smoking and decrease people's ability to stop smoking, whereas atypical antipsychotics decrease basal smoking and promote smoking cessation. However, we found that the data available were generally of moderate quality and from small studies, and that there were conflicting findings. The review also critically assesses a number of potential mechanisms for this effect: the use of smoking as a form of self-medication for the side effects of antipsychotics, the effect of antipsychotics on smoking-related cues and the effect of antipsychotics on the appreciation of the economic cost of smoking behaviour. Gaps in the research are noted and recommendations for further study are included. More study of this important issue is needed to clarify the effect of antipsychotics on smoking behaviours.

Effects of risperidone on development and expression of nicotine-induced locomotor sensitization in rats

It has been shown that atypical antipsychotics significantly reduce smoking and alcohol consumption in schizophrenic patients. However, our knowledge about the effect of risperidone, especially on nicotine abuse is limited. We aimed to test the effects of risperidone in an animal model of nicotine-induced locomotor sensitization, which represents initial neuroadaptations and continued behavioral changes in nicotine-type dependence. To investigate the effect of risperidone on the development of nicotine-induced locomotor sensitization, rats were pretreated with risperidone (0.025 and 0.050 mg kg⁻¹) 30 min before the nicotine (0.5 mg kg⁻¹, base) treatment, and locomotor activity was recorded for 30 min. This procedure was repeated every day for eight sessions. After a 6-day drug-free period, rats were challenged with nicotine (0.5 mg kg⁻¹). To reveal the effect of risperidone on the expression of nicotine-induced locomotor sensitization, rats were injected with nicotine for eight sessions. After a 6-day drug-free period, rats were pretreated with risperidone (0.025 and 0.050 mg kg⁻¹) or vehicle 30 min before the nicotine (0.5 mg kg⁻¹) challenge injection. Repeated administration of nicotine generated robust locomotor sensitization in rats. Risperidone pretreatment (0.050 mg kg⁻¹) blocked the expression but not the development of nicotine-induced locomotor sensitization in rats. Our results suggest that risperidone blocks the continuation of nicotine-type addictive behavior, but it is ineffective on early adaptations in the initiation of nicotine addiction. Thus, this drug may have a limited beneficial effect in treatment of nicotine dependence.