Paul Erdős was a somewhat eccentric mathematician who was known to use stimulants and eventually amphetamines. He was quite adept at solving problems, had a prolific work rate and made meaningful contributions in various branches of maths.

A friend bet him he couldn't quit amphetamines for month so he did. His response at the end of the month?

"You've showed me I'm not an addict. But I didn't get any work done. I'd get up in the morning and stare at a blank piece of paper. I'd have no ideas, just like an ordinary person. You've set mathematics back a month."

So there's no one specific thing he developed under the influence of drugs but arguably everything he came up with in the last 20 years of his life was apparently helped by the influence of amphetamines.

Augustus Owsley "Bear" Stanley conceptualized the Wall of Sound, while analyzing an existing system during an LSD induce episode of synethesia (mixing of the senses). Stanley was also crackpot, a Kentucky political family's scion, and (odds overwhelmingly are) the maker of some of Mullis's LSD. (And one of my favorite historical figures.)

Source: "Grateful Dead Gear," by Blair Jackson

Francis Crick claimed that he figured out the double helix structure of DNA while he was under the influence of LSD. He was quite the devotee of the drug, which he claimed he used to enhance his thinking. Considering it helped him win a Nobel Prize, it's hard to argue with that idea.

Kary Mullis, the creator of Polymerase chain reaction for which he won a Nobel Prize in Chemistry, was known and had admitted to using LSD frequently and had stated that LSD probably helped him with this.

This was first mentioned to me by my professor in a university biology course. Mullis has also spoken about this a few times in interviews / Q&A's.