Marijuana is a primary cause of substance use disorders around the world. In the United States, over 60% of all Americans aged 12 and older who have an illegal drug-related substance use disorder abuse or are dependent on marijuana. In the U.S. more teens are in treatment with a primary diagnosis of marijuana dependence than all other illicit drugs combined.
Early marijuana use is particularly dangerous. Research has shown that adults age 18 and older who first started using marijuana use at age 14 or younger were most likely to have abused or been dependent on illicit drugs in the past year. Additionally, adults who first used marijuana at or before age 14 were six times more likely to have a substance use disorder than those who initiated marijuana use at age 18 or older (12.6% vs. 2.1%) and two times more likely than those who initiated marijuana use between the ages of 15 and 17 (12.6% vs. 6.6%).
Preventing youth marijuana use will decrease the likelihood of later substance use disorders and also decrease initiation to other illegal drug use. Youth who use marijuana are more likely to have higher rates of other illegal drug use  and to develop abuse and dependence. A recent study of French adolescents showed that among marijuana users, the risk for other illicit drug use was 21 times higher among experimental marijuana users and 124 times higher among daily marijuana users than non-users.
There are serious short- and long-term effects of marijuana use, particularly heavy chronic marijuana use, including deficits related to the brain, cognitive function, attention, et al.       Marijuana use is associated with lower academic achievement and associated with increased rates of dropout.   Marijuana contains about four times as much tar and 60% more cancer-causing chemicals than cigarettes. Most concerning is the growing body of research showing an association between early marijuana use and the development and worsening symptoms of schizophrenia.  
The harms of marijuana use extend beyond the individual users. U.S. rates of drugged driving show that marijuana is the most prevalent drug found among randomly stopped drivers and among fatally injured drivers. A recent international meta-analysis of studies confirms the danger of marijuana use amongst drivers in that marijuana use doubles the risk for crash. 
With a growing number of global efforts supporting “medical marijuana” and marijuana legalization, marijuana-based initiatives must be effectively combated with knowledge about the serious consequences of marijuana use.
Of course other drugs cause terrible harm as well. Why is marijuana the most dangerous drug? Use of other drugs, such a cocaine, methamphetamine, heroin and Ecstasy cause dramatic negative consequences, called “bottoms” that sooner or later – and often sooner – force the users to confront the folly of their drug use. Marijuana use, in contrast, commonly saps the users’ motivation and determination. The losses with marijuana are tied to caring about people and goals. Not all users experience this effect but many do leading to the conclusion that marijuana causes users to become “stupid and lazy”, terms readily accepted by people who have been heavy marijuana users once they have stopped use. Marijuana is also called the “careless” drug because it causes any users to care less about the things they cared a lot about before beginning using the drug.
For more information marijuana and its effects, visit:
– Office of National Drug Control Policy’s Marijuana Resource Center: www.whitehouse.gov/ondcp/marijuanainfo
– National Institute on Drug Abuse: www.drugabuse.gov
– Prevent Teen Drug Use: www.PreventTeenDrugUse.org
Robert L. DuPont, M.D.President,
Institute for Behavior and Health, Inc.