The gateway concept is one that generates a lot of controversy. The research is not yet settled but it suggests that while most people who smoke marijuana do not go on to use other drugs, most teens who use other illegal drugs try marijuana first. For example, the risk of using cocaine is much greater for those who have tried marijuana than for those who have never tried it. However, this is also true for alcohol and tobacco. Animal studies suggest that—because the teen brain is still developing—early use of marijuana alcohol or tobacco may alter the brain’s reward system, putting teens at higher risk of using other drugs. In addition, using marijuana puts children and teens in contact with people who use and sell other drugs, increasing the risk of additional drug use.