Fifteen patients with psoriasis who were taking lithium were randomly assigned to receive, in double-blind fashion, 6 g/day of inositol or placebo for 10 weeks. After a 4-week washout period, each patient received the alternate treatment for an additional 10 weeks. The severity of psoriasis, as determined by the Psoriasis Area and Severity Index (PASI) score, was assessed at the beginning and end of each treatment period. The median PASI score decreased (improved) by 35% during treatment with inositol, whereas the score increased (worsened) by 63% during treatment with placebo (p = 0.015 for the difference in the change between treatment periods). Thirteen of 15 patients improved while receiving inositol, compared with 7 of 15 during treatment with placebo. In 11 other psoriasis patients who were not taking lithium, there was a nonsignificant trend toward a worse outcome with inositol, compared with placebo.

Comment: Treatment with lithium carbonate can trigger or exacerbate psoriasis. The therapeutic effect of lithium in bipolar disorder appears to be mediated by a depletion of inositol. Supplementation with inositol has been shown to reduce some of the adverse peripheral side effects of lithium (such as polyuria), without reducing its beneficial central effects. The results of the present study indicate that inositol is beneficial in the treatment of lithium-induced psoriasis, but does not improve psoriasis in people not taking lithium.

Allan SJR, et al. The effect of inositol supplements on the psoriasis of patients taking lithium: a randomized, placebo-controlled trial. Br J Dermatol 2004;150:966-969.