The chemical nepetalactone is to credit for your kitty's crazy reaction to catnip. The chemical, which is a mild hallucinogen, doesn't affect humans in the same sense as we do not rely as heavily on our noses as cats do. In fact, it doesn't even affect all cats.
Finasteride is a drug that belongs to the class of androgen inhibitors, which means that it blocks the production of male sex hormones. It is sold in the United States and Canada under the brand names Proscar and Propecia.
Finasteride (which is the active chemical in Propecia) was first developed by Merck to treat enlarged prostates in men. Finasteride works by inhibiting (slowing down/stopping) the enzyme that converts testosterone to DHT (the hormones primarily responsible for hair loss through hair follicle miniaturisation). That enzyme is called 5-alpha-reductase.