Drugs are at Wellesley, just like everywhere else, and they can be sought after or ignored. Depending on where students hang out and who their friends are, some report never having smelled marijuana smoke wafting down the hall, while others see classmates toke up on a daily basis. Drugs that help people concentrate, from caffeine to Adderall and Ritalin, are both used and abused, but it's hard to determine how widespread this practice is.
It's not likely that you're going to stumble into the bathroom at a Wellesley party and find someone doing hardcore drugs, and it's even less likely that people are going to miss class because they just can't resist the "wake and bake." On the other hand, the desire to conform to—or escape—academic pressure may tempt some students to pop an Adderall while writing a paper or smoke a little to blow off steam on the weekend.