Getting high on anything is going to temporarily affect your ability to learn while your high, or shortly after. Alcohol, pot, anything. But not permanently, the affect is gone in hours after your buzz if your healthy.

If you want to really be sharp, you also need a good diet and good daily exercise. Good exercise has been proven time and again to sharpen learning ability, memory and agility both mentally and physically and lower stress levels, and a good diet is proven to help as well.

Get high in moderation, not when you need to study, and walk or run a mile or three or something daily to get your muscles working and your heart thumping and eat good and you'll be better off than 90% of people out there.