The drug scene is not very prominent on the UC Davis campus. There is a zero-tolerance policy for drugs and alcohol, and because of the huge student body, the actual percentage of hard drug users is relatively low. Besides caffeine and alcohol, marijuana is the most popular drug of choice, followed by prescription "study drugs," like Adderall, which make a strong appearance during midterms and finals weeks.
Even though the drug use is pretty low-key and unnoticeable, it is still existent and not hard to come across if that is what you are looking for. There is no peer pressure to do drugs and drink, and people trying to avoid that sort of stuff note that they still have a thriving social life without it. On the other hand, drugs are not difficult to come across if you are looking for them. It is easy to find a group of people with similar interests, making drugs easy to find or easy to stay away from, depending on whom you choose to surround yourself with.