Phenobarbitone has been reported to decrease the gastrointestinal absorption of griseofulvin. Griseofulvin may increase the rate of metabolism and diminish side effects of some drugs such as coumarin anticoagulants and oral contraceptives. Use of an alternate or additional means of contraception if taking oestrogen-containing oral contraceptives concurrently with griseofulvin and for one month after stopping griseofulvin therapy is advisable. Griseofulvin has also been reported to reduce the plasma concentrations of salicylate in patients taking aspirin.
Since griseofulvin is derived from a species of Penicillium, it is theoretically possible that patients intolerant to penicillins or penicillamine may be intolerant of griseofulvin also. However, cross-sensitivity between griseofulvin and penicillins or penicillamine has not been clinically substantiated. In addition penicillin-sensitive patients have received griseofulvin without difficulty.