A physical enhancer enhances some physical aspect predominantly, and a mental enhancer enhances some mental aspect predominantly or allows you to do better at enhancing the particular aspect yourself.

physical enhancers I can think of: Steroids, Viagra

mental enhancers I can think of: Modafinal (and similar, mainly, can also argue it is a physical enhancer), psychological drugs focused on better focus etc.

half and half - amphetamines. you can stay up to study but you don't pay attention so you could also stay up to party.

physical enhancers I can think of offhand: drug makes you beautiful, drug makes you physically tough, sharpshooter drug etc. etc.

mental enhancers I can think of: increase short term memory, photographic memory, increase reading speed, language processing improvements.

I guess I see that passing the GED drug mentioned in the other comment but intelligence is as a general rule not something people aspire to in this society (IMHO) therefore I would expect intelligence altering drugs would not receive as much funding as drugs that effect the things that society values, and those things tend to be physical.

Or to paraphrase Idiocracy the best minds would be devoted to enlarging penis size not making people smarter.