N-Acetyl Cysteine (NAC) for Substance Use Disorder

NAC has a credible mechanism and some positive small trials for craving, particularly in cannabis use in younger people, but larger trials have been inconsistent.

NAC restores cystine-glutamate exchanger function in the nucleus accumbens, normalising extrasynaptic glutamate tone that becomes dysregulated after chronic drug exposure and drives cue-induced craving.

The glutamate hypothesis of addiction gave NAC an unusually specific rationale, and early trials were encouraging: a randomised trial in cannabis-dependent adolescents found higher rates of negative urine screens with NAC added to contingency management. Subsequent work has been less consistent — a larger multi-site trial in cannabis-dependent adults did not replicate the effect, and results across cocaine, methamphetamine and nicotine have ranged from modest benefit to null. Meta-analyses generally conclude that NAC may reduce craving with a small effect size while evidence for changing actual use is weak. NAC is inexpensive and well tolerated, so it is a defensible adjunct in someone already receiving proper treatment, but it is not a substitute for medication-assisted treatment or behavioural therapy.

Trials in adults with long-standing dependence have been largely negative; the strongest signals were in younger people with shorter use histories.