This recent study shows how stimulants reduce the benefits of sleep to store long term memories. They are counter-productive for study and as a general aid to people struggling with memory. They only help during the same day of study.

https://www.latimes.com/socal/daily-pilot/news/story/2019-09-10/non-prescribed-stimulants-may-improve-short-term-focus-but-fail-users-in-the-long-run-uci-researchers-say[/URL]