The alleged interaction between MAOIs
and most antihistamines
appears to be based on a single animal study, and is probably more theoretical than real. The exception seems to be cyproheptadine and promethazine (see below).
The UK manufacturers of most of the sedating antihistamines
(alimemazine, brompheniramine, chlorphenamine, diphenhydramine) state that MAOIs
may intensify the antimuscarinic effect of antihistamines
, and many contraindicate or caution concurrent use.