According to the
NCAA's description of its drug testing program, the NCAA conducts year-round testing of performance enhancing drugs (PED) but not recreational or "street" drugs (I think marijuana and heroin are considered "street" drugs but cocaine is considered a PED by the NCAA). The NCAA tests for all substances only during NCAA championships:
The program involves urine collection and laboratory analyses for substances on a list of banned-drug classes developed by the NCAA Board of Governors.
This list consists of substances generally purported to be performance enhancing and/or potentially harmful to the health and safety of the student-athlete.
Notably:
•Student-athletes are held responsible for use of all banned substances at all times
•The NCAA year-round testing program may test for anabolic agents, diuretics and masking agents, peptide hormones, beta-2 agonists and beta blockers. Stimulants and street drugs are generally not tested in NCAA year-round testing.
•The NCAA championship testing program may test for all banned drug classes, and include tests for street drugs and stimulants.
•Other testing occasions, such as exit tests, follow-up tests and suspected manipulation, may include testing for all banned drug class.