Marijuana use also has adverse effects on the lungs, on male and female sexual function, and on the cardiovascular system. In pregnant women using marijuana, the fetus is exposed to THC through the placenta and umbilical cord, receives less oxygen, and has a higher risk of birth defects.
Approximately 9% of users develop an addiction to marijuana, but that nearly doubles to 17% among users who start in adolescence, according to the National Institute on Drug Abuse.
“The earlier they are when they start, the more likely they are to develop an addiction,” Dr. Schizer said, pointing out that 88% of all substance abuse treatment admissions among adolescents aged 12-17 years involved marijuana, according to 2012 Substance Abuse and Mental Health Services Administration data. By age 21 years, approximately 4% of users are addicted, but about a quarter to half of daily users develop an addiction. Further evidence of marijuana’s addictiveness are “bona fide withdrawal symptoms,” which typically peak about 10 days after last use, and can include restlessness, anxiety, increased irritability or aggression, difficulty falling and staying asleep, nightmares or strange dreams, decreased appetite, and weight loss.
Driving impairment under the influence of marijuana results from poorer attention, worse working memory, lack of coordination, poorer reaction time, and lack of visual perception caused by THC. In a graphic Dr. Schizer presented comparing Colorado to 34 states without medical marijuana, the proportion of drivers testing positive for marijuana in fatal crashes began sharply increasing in 2009, the year widespread medical marijuana was implemented in Colorado.
“In particular, we are thinking about relatively inexperienced drivers, so the effects are even more important,” Dr. Schizer said.
Medical marijuana
What began as an Institute of Medicine recommendation for “compassionate use” to relieve suffering in terminally ill patients has become a movement to medicalize marijuana despite limited evidence of its therapeutic benefits, Dr. Schizer explained. Since California legalized medical marijuana in 1996, many other states have followed suit. Yet the only condition for which modest evidence supports its use is treating adults’ nausea and vomiting resulting from chemotherapy. For chronic pain, anorexia associated with HIV/AIDS, and neurologic problems such as multiple sclerosis, the evidence is not sufficient to show therapeutic efficacy, and no studies have looked at medical marijuana use in children.
“Marijuana is not a medication,” Dr. Schizer said. “There is therapeutic potential in these cannabinoids, but that’s not the same as directing patients to using medical marijuana. We know that penicillin was originally derived from mold, but you would give patients penicillin, not a slice of moldy bread” to treat a bacterial infection.
Actual medical cannabinoids approved for treatments include Marinol and Sativex. The Food and Drug Administration has approved Marinol, a slow-acting oral formulation, to treat weight loss in patients with anorexia or AIDS and to treat nausea and vomiting from chemotherapy. Ongoing phase III clinical studies are testing Sativex for the treatment of advanced cancer pain. To suggest that a patient use commercially available marijuana therapeutically would be akin to sending patients to an opium den instead of prescribing a precise opioid for pain, Dr. Schizer suggested. “I think it’s unconscionable for doctors to prescribe something that is smoked.”
Data from Colorado and Oregon suggest few individuals with medical marijuana cards may be using it for serious illnesses, Dr. Schizer pointed out. Less than 2% of medical marijuana cardholders report cancer, HIV/AIDS, glaucoma,i or multiple sclerosis as their reasons for using marijuana. The typical profile of a cardholder is a 32-year-old white man with a history of alcohol and cocaine abuse and no history of life-threatening illnesses, she said. According to the Colorado Department of Public Health and Environment, 12% of medical marijuana users report using it for severe nausea, 17% for muscle spasms, and 94% for “severe pain.”
Meanwhile, Colorado’s legalization of recreational marijuana imparts several lessons, Dr. Schizer said. The highest rate of teen marijuana use in the United States occurs in Denver, and 11% of teens report using marijuana in the past month, compared with a national average of 8%. Drug-related school suspensions have increased, and the rate of car crashes in which the driver tested positive for marijuana tripled between January 2014, when stores opened, and April 2014.
Dr. Schizer reported no relevant financial disclosures.