<p>I’ve heard of using n-acetyl cysteine (a dietary supplement) for habits such as nail biting, skin picking, and hair pulling (trichotillomania). There are actually a couple of peer reviewed journal articles on its efficacy, including one clinical trial in archives of general psychiatry last year ([Arch</a> Gen Psychiatry – Abstract: N-Acetylcysteine, a Glutamate Modulator, in the Treatment of Trichotillomania: A Double-blind, Placebo-Controlled Study, July 2009, Grant et al. 66 (7): 756](<a href=“http://archpsyc.ama-assn.org/cgi/content/abstract/66/7/756]Arch”>N-Acetylcysteine, a Glutamate Modulator, in the Treatment of Trichotillomania: A Double-blind, Placebo-Controlled Study)). May be worth a try…</p>