<unk>  has been known to decrease the effects of hormonal birth control, sometimes to the point of uselessness. Being chemically related to phenobarbital, it might also do the same thing to digitoxin, a cardiac glycoside.
Amobarbital
Heptobarbital
Pentobarbital
Ethallobarbital
Secobarbital
Hexobarbital
Butobarbital
Phenobarbital