Quetiapine Pharmacotherapy for Cannabis Dependence

In a 12-week randomized double-blind placebo-controlled clinical trial, we will evaluate the efficacy of quetiapine for the treatment of marijuana dependence in 150 outpatients. Participants will be randomly assigned to treatment under double-blind conditions with either a fixed dosing schedule of quetiapine or placebo. All participants will receive Medical Management, a medication adherence focused psychosocial intervention that facilitates compliance with study medication and other study procedures, and promotes abstinence from marijuana and other substances. All participants will receive progressive voucher incentives for compliance with study visit attendance and completing other study procedures, with the objective of achieving a highly compliant sample. The results of a dose-finding pilot study of quetiapine for the treatment of marijuana dependence (see Preliminary Studies) suggests that the ideal dosing for the proposed project is a single 300 mg dose every evening, achieved after a gradual three-week titration. Clinical experience with this medication for treatment of marijuana dependence indicates that a gradual upward titration of dose is advisable to maximize tolerability and that morning dosing was poorly tolerated. Quetiapine (immediate release formulation) will be administered in 25 and 100 mg capsules; placebo capsules will appear identical to the quetiapine capsules. Participants in both treatment arms will take the same number of pills on the same schedule. Study medication will be dispensed on a weekly basis starting with the baseline visit. Quetiapine will be titrated over a three-week period to the target dose of 300 mg or the maximum tolerated dose. The research psychiatrist will make dose reductions for tolerability if necessary.