Creatin used to be a thing didn’t it? And I think you can that over the counter.
It has well researched benefits but it won’t turn you into superman like drugs will.
I recall someone else experimenting with a number of banned substances to see what improvements they made. At the end of it he concluded that the one thing he would like to be able to take was Human Growth Hormone. Once he started on that he was also able to stop using his reading glasses and didn’t feel any ill effects. Most of the other stuff had unpleasant side effects.
Drugs – A Cautionary Tale
HGH does sound like the drug you’d want to take.
There’s other ways to maximise what nature gives you too though. If you believe Tim Ferris’s then there’s mileage in a high cholesterol diet as it’s required to synthesise testosterone in the body.
Then there’s the “I’m not sure if it’s illegal but it’s not natural” stuff like GABA, which IIRC results in increased HGH levels. Also gives you a nice tingly sensation and the best nights sleep ever!
My housemate used to do this stuff, he was always built like a brick shithouse so between the supplements and his gym routine something was working. Then he went all out with the drugs and the gains were an order of magnitude!
Stopping smoking, riding more, fueling your body with sports drinks whilst riding, caffeine, or getting n E-bike are probably more effective though. I don’t usually use carb drinks, so when I take one on a long ride it certainly feels like rocket fuel!
[edit] basically what they said while i was typing