N-acetylcysteine is an antioxidant which modulates the glutamate system in the brain. Glutamate is actually the most prevalent neurotransmitter in the brain, and generally has strongly activating effects on nerve cells.
A recent study in Archives of General Psychiatry described groups of individuals with compulsive hair-pulling behavior (trichotillomania), randomized to receive either placebo, or N-acetylcysteine 1200 mg/day, then up to 2400 mg/day, over 12 weeks:
The N-acetylcysteine group had about 50% reduction in hair-pulling behaviour, with no change in the placebo group. Those in the N-acetylcysteine group did not report any side effects. In fact, the only side effects were among those in the placebo group.
The same author published a study in 2008 showing a substantial improvement in compulsive gambling behavior in a group given NAC at an average dose of about 1500 mg/d:
A very preliminary study showed that NAC may have some promise in treating cocaine addiction:
NAC has shown some promise as an adjunctive treatment for chronic schizophrenia; in this study the dose was 1000 mg twice daily, over 24 weeks. Once again, there were no side-effects. As I look at the body of the paper, I see that there was a definite favorable effect from the NAC compared to placebo, in several domains, but the size of the effect seemed clinically modest:
So NAC appears to be an appealing therapy for a variety of frequent, and often difficult-to-treat psychiatric symptoms. There do not appear to be side effect problems.
At this point, NAC can be obtained from health food stores in Canada, as a nutritional supplement. It is also on the prescription formulary in an injectable form for treating acetaminophen toxicity.