1. Translational Addiction Research Laboratory, Centre for Addiction and Mental Health, 33 Russell Street, Toronto, Canada M5S 2S1 and INSERM U894-Team 1, Centre for Psychiatry and Neurosciences, 2ter rue d'Alesia, 75014 Paris, France. E-mail:
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Liebrenz et al. [1] suggested that agonist substitution could be an alternative for some benzodiazepine-dependent patients. In their thoughtful review, they compared the current usual treatment of benzodiazepine-dependent patients with the approach used in opiate dependence since the early 1960s, for which agonist therapy is considered as the gold standard.

The use of nicotine replacement in nicotine-dependent smokers also supports the hypothesis that agonist treatment can be useful in the management of substance users other than opiates. The efficacy of smoking cessation medication in supporting abstinence appears to be related directly to its ability to suppress withdrawal symptoms [2]. Furthermore, some evidence suggests that delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, decreased withdrawal symptoms in cannabis-dependent patients [3–5], whereas various non-agonist treatments showed a lack of efficacy (for a recent review, see [6]).

Nicotine replacement treatment and methadone do not usually give users a great deal of positive reinforcement for continued use, but rather prevent the negative reinforcement of withdrawal. Similarly, THC is not highly reinforcing in itself, even in chronic users [7], which might be a factor in successful agonist treatment that leads eventually to abstinence. In any case, the use of an oral form of THC might be expected to avoid the pulmonary complications of smoking cannabis [8].

While these results remain preliminary, they suggest that the effectiveness of agonist treatments is well known in both opiate and nicotine dependences and warrant further research, not only in benzodiazepine dependence, as suggested by Liebrenz et al., but also in cannabis dependence.

Declaration of interest

The author is funded by a grant from the Société francaise de tabacologie (SFT) and the Addiction Program of CAMH.