Say what? By that I'm hoping you mean that drugs are limited by their structure for transdermal administration (small and lipophilic will diffuse through the skin's membrane fairly easily). Being that it bypasses first-pass hepatic metabolism, drugs that fit the bill will have a higher availability than those drugs taken orally.
However, I do agree Forskolin should probably just be taken orally. I would never try to make my own transdermal patch and there's really not much of a reason to do so in the first place.