A study that tracks when college students first try drugs and alcohol finds June is the most popular month for initiating marijuana and alcohol use. Winter is the peak season for full-time college students to start using prescription drugs, such as stimulants and pain relievers, in non-medical ways.

Researchers used data from the Substance Abuse and Mental Health Services Administration’s (SAMHSA) National Survey on Drug Use and Health, which includes information on full-time college students, the Associated Press reports. The study found 383,000 students tried marijuana for the first time in the past year, with June being the most popular month. About 450,000 underage full-time college students started drinking in the past year, with June also being the most common month for a first alcoholic drink, the article notes.

About 251,000 college students started using pain relievers non-medically in the past year, with December being the most frequent time to start. The 137,000 students who used stimulants, such as Adderall or Ritalin, nonmedically were most likely to start in November. December and April were also peak months for non-medical use of stimulants. November, December and April are months in which many college final exams and midterms occur, SAMHSA noted in a news release.

Students may believe Ritalin or Adderall will help them improve their academic performance, although there is no medical evidence of this, the article notes.

“These findings show that college students are vulnerable to substance use at any time – not just when they are away at school,” said SAMHSA Acting Administrator Kana Enomoto. “That means that parents, college counselors, faculty members, staff, mentors, and other concerned people must take every opportunity to talk with college students about the risks of substance use and where they can turn to for help.”