Retention rates in two naltrexone programmes for heroin addicts in Vitoria, Spain.

The main finding of a former Spanish multicenter study (SMS) on the effectiveness of naltrexone maintenance in heroin addicts, was the high retention rate achieved at 24 weeks of follow-up since naltrexone induction (40%). The authors claimed this rate was one of the highest ever reported in the literature for a non-selected sample of opiate addicts and discussed the possible relevance of a set of variables - like motivations and expectations due to a new treatment - on the findings. To assess the possible effects of these variables, we have compared the retention rates in two similar naltrexone programmes.