Are there any known interactions between cannabis inhalation and risperidone (Risperdal)?/nA 19-yea

Fråga: Are there any known interactions between cannabis inhalation and risperidone (Risperdal)?

A 19-year-old male, regular user of inhaled cannabis, took a first dose of 0.25 mg risperidone, because of schizophrenic behaviour. The following day he had a more aggressive behaviour and agitation than usual and his doctor wonders if this can have been due to an interaction between inhalation of cannabis and risperidone.

Sammanfattning: No interactions between cannabis and risperidone has been found.

The cause if this patient´s agitation and aggressiveness can possibly be attributed to a side effect of risperidone or to the clinical situation of the patient.

Svar: There are no reports at present of pharmacokinetic or pharmacodynamic interactions between risperidone and cannabis.

Risperidone is a neuroleptic used mostly for the treatment of schizophrenia. Risperidone is metabolised mainly in the liver by CYP2D6 to a metabolite (9-OH-risperidon) that is just as active as the mother compound. Risperidone and its metabolite have a conjoint half-life of 20-24 hours (1). In FASS 2005 (the Swedish catalogue of approved medical products), agitation is reported as an usual side-effect (>1%) (2). In the Micromedex database, agitation and aggressiveness are reported to be experienced by >1% of the patients treated with risperidone (3).

Cannabis is metabolised partially by CYP3A and possibly also by CYP2C9. The tar existent in tobacco can induce CYP1A2, which also may be possible with cannabis inhalation (4). Since different cytochromes are involved in the metabolism of risperidone and cannabis, a pharmacokinetic interaction between them is seen as improbable as a cause of high or low blood concentrations of either drug. These interactions have however been described when neuroleptics metabolised by CYP1A2 are used combined with cannabis (5). Hardman JG, Limbird LE, Goodman Gilman A, editors. Goodman & Gilman´s The pharmacological basis of therapeutics. 10th ed. New York: McGraw-Hill; 2001

Fass 2005
Risperidone. Drugdex(R) System; Thomson MICROMEDEX, Greenwood Village, Colorado (cited 2005-04-11)
Drugline no 16518 (year 2000)

Zullino DF, Delessert D, Eap CB, Preisig M, Baumann P. Tobacco and cannabis smoking cessation can lead to intoxication with clozapine or olanzapine. Int Clin Psychopharmacol 2002;17(3):141-3. (abstract)