Ongoing studies of teenagers and their drug use patterns show that very few use other drugs without first trying marijuana. For instance, the risk of using cocaine has been estimated to be more than 100 times greater for those who have tried marijuana than for those who have never tried it. To date, there have been few studies on factors associated with this so called gateway theory of drug use and dependence, but growing evidence suggests a combination of biological, social, and psychological factors are involved.

Research published in the January 22, 2003 issue of the Journal of the American Medical Association is the first major attempt to tease apart the genetic and environmental factors that predispose young marijuana users to develop subsequent problems with other, more dangerous drugs.

The findings suggest that children who used marijuana before age 17 were much more likely to go on to other drugs and to have alcohol or drug dependance problems compared to their twins who did not use marijuana before the age of 17.

About the Study

Researchers in Australia studied 311 twins (622 individuals) who participated in the Australian Twin Register. These men and women (average age 30 years) were telephoned by the researchers and asked questions about their non-medical drug use: specifically about the initiation and frequency of the drug use and related problems.

Question on factors associated with an increased risk of using marijuana and other drugs (like psychiatric disorders and early tobacco or alcohol use) were also asked. The researchers then calculated the odds of later drug use and dependence if a person started smoking marijuana before the age of 17.

The Findings

The majority of those who reported both marijuana and other drug use said that they started using marijuana before using other drugs. Compared to their twin who had not used marijuana before the age of 17, those who had used marijuana by this age were 2.1 to 5.2 times more likely to have reported drug use, illicit drug abuse or dependence, and alcohol dependence.

By using twins, the researchers were able to adjust for genetic and a number of environmental factors that could have influenced initiation of marijuana and other drug use. This allowed them to get a better understanding of the role that early marijuana use might play in later drug use and dependence.

How Does This Affect You?

The results of this study suggest that marijuana use before the age of 17 is an independent risk factor for later illicit drug use and dependence. Although the reason for marijuana’s role as the gateway to future drug use is unclear, researchers speculate that young marijuana users simply have ready access to dealers of harder drugs.

These results highlight the need to support programs designed to prevent or stop the use of marijuana in adolescent populations. The National Institute on Drug Abuse has made the following recommendations to help parents and others who interact with at-risk teens recognize the signs and symptoms of marijuana use.

Signs that someone may be high on marijuana:

  • Dizziness and having trouble walking
  • Silly and giggly for no reason
  • Red, bloodshot eyes
  • Problems remembering things that just happened

Other signs that a teen may be using marijuana or other drugs:

  • Withdrawal
  • Depression
  • Fatigue
  • Carelessness with grooming
  • Hostility and deteriorating relationships with family members and friends
  • Changes in academic performance
  • Increased absenteeism or truancy
  • Lost interest in sports or other favorite activities
  • Changes in eating or sleeping habits
  • Signs of drugs and drug paraphernalia, including pipes and rolling papers.
  • Odor on clothes and in the bedroom
  • Use of incense and other deodorizers
  • Use of eye drops
  • Clothing, posters, jewelry, etc., promoting drug use

Note: Keep in mind that these signs may also indicate problems other than drug use (depression for instance). The key is to keep the lines of communication open and to remain as active as possible in the lives of your teenage children or students.