Marijuana is the most commonly abused illicit drug in the United States. While marijuana use declined in the 1980s, its use among all youth—including college students—rose steadily in the 1990s. Starting in 2000, reports of marijuana use among college students started to level off, with the annual prevalence hovering between 30 percent and 35 percent for several years. In addition to recognizing marijuana's short- and long-term effects, prevention advocates raise concerns that marijuana may be a "gateway" drug, introducing students to an illicit drug culture and exposing them to users of other kinds of drugs.

As with alcohol and other illicit drugs, the possible dangers of marijuana use cannot be overlooked. Frequent use can be both physically and psychologically addictive and is a common cause of social and behavioral problems.

Some of the long-term consequences of frequent marijuana use include:

  • an increased tolerance for the drug
  • depression and anxiety
  • impaired memory and learning
  • loss of coordination
  • impaired immune defense
  • complications in pregnancy
  • frequent respiratory infections
  • increased heart attack risk
  • increased risk for lung and respiratory tract cancer

Marijuana users also demonstrate an increased risk for other high-risk behaviors such as heavy drinking and cigarette smoking when compared with their peers who abstain from marijuana. Additionally, students who use marijuana frequently may function at a limited intellectual level at all times—that is, even when not under the influence of the drug—contributing to lower grades and an increased risk for dropping out of college.

In 2004, the Office of National Drug Control Policy released an Open Letter to Parents endorsed by the American Academy of Family Physicians and the Partnership for a Drug-Free America, in which they articulated the effects of marijuana use on students' academic success. According to the letter, frequent marijuana use can affect students' concentration and ability to retain information. The Substance Abuse and Mental Health Services Administration's National Household Survey on Drug Abuse found that, compared with students who earn an average grade of A, students averaging a D or lower are four times more likely to have used marijuana in the last year.

Many marijuana users do not realize that, as with other illicit drugs, it can be addictive. While not everyone who uses marijuana becomes dependent upon it, thousands of people who enter drug treatment programs annually report marijuana as their primary drug of abuse. Additionally, marijuana users report withdrawal symptoms similar to those associated with heroin, cocaine, and alcohol.