Psychiatrists regard the histamine-receptor antagonism of antipsychotics mostly as a nuisance given its relationship to sedation and weight gain. Some evidence, including research on animal models and preliminary human investigations, suggest that in fact it has a therapeutic role for schizophrenia. Recent research has found that clozapine is an inverse agonist at H2 receptors, meaning that it reduces H2 receptor activity below its baseline (1).
A Finnish team has completed a four-week randomized, controlled, and double-masked trial of famotidine, a selective H2 antagonist now marketed as an over-the-counter remedy for heartburn (2). They recruited 30 patients with treatment-resistant schizophrenia, mean age about 51 years, who were on a variety of antipsychotics and had residual functional impairment; 11 of them were on clozapine. They assessed them with the Scale for Assessment of Negative Symptoms (SANS), the Positive and Negative Syndrome Scale (PANNS), and the CGI. The active-treatment group received 100 mg of famotidine twice daily; no significant adverse reactions occurred, but 3 subjects receiving placebo dropped out “for unclear reasons.”
In comparison with the placebo group, the famotidine group had a significant reduction in mean PANSS total score and PANSS general subscale score and in mean CGI. The mean total PANSS score decreased 11% in the famotidine group and 1% in the placebo group. The researchers acknowledged that their study was too brief and had too few subjects to adequately investigate famotidine, and they suggested a follow-up trial with at least 80 subjects for 8 to 10 weeks to test the potential of this well-tolerated medication in treatment-resistant patients.
1. Humbert-Claude M, Davenas E, Gbahou F, et al. Involvement of histamine receptors in the atypical antipsychotic profile of clozapine: a reassessment in vitro and in vivo. Psychopharmacology. 2012;220:225-241.
2. Meskanen K, Ekelund H, Laitinen J et al. A randomized clinical trial of histamine 2 receptor antagonism in treatment-resistant schizophrenia. J Clin Psychopharmacol. 2013;33:472-478.