April 28, 2015
Originally appeared in in Alcoholism and Drug Abuse Weekly, April 27, 2015.
Photo of marijuana spilling from a prescription bottle

Opinion on marijuana has changed dramatically in the United States. The public increasingly perceives it as a benign substance, and there is growing interest in its potential medicinal uses. Already almost half of the states have medical marijuana laws, and congressional bills have recently been proposed that would reschedule the drug to reduce hindrances to research and facilitate marijuana’s use as medicine.

Advocates tout marijuana as a miracle drug with a wide range of potential therapeutic uses, while public health voices raise alarms about its dangers if made more widely available. The science justifying either position is often not as robust or clear as its partisans would wish. Marijuana’s impact on lung cancer remains unclear, for instance, but so does its actual range of medicinal benefits. The urgent need for more research is something all sides in the current marijuana debate can agree on. Policy changes around marijuana will need to be informed, as much as possible, by science.

There is solid evidence that the main psychoactive ingredient in marijuana, THC, is effective at controlling nausea and boosting appetite. There is also some preliminary evidence that THC or related cannabinoid compounds such as cannabidiol (CBD) may also have uses in treating autoimmune diseases, inflammation, pain, seizures and psychiatric disorders, including substance use disorders. Despite claims of marijuana’s usefulness in treating post-traumatic stress disorder, supporting data is minimal, and studies have not investigated whether symptoms may worsen after treatment is discontinued.

We do not yet know all the ways chronic treatment with marijuana or marijuana-derived compounds could affect people who are rendered vulnerable either by their illnesses or by their age. We also don’t know how medical marijuana laws will affect other aspects of public health and safety. For example, wider medical marijuana use could potentially impact driver safety, as both laboratory and epidemiological research link recent marijuana use to increased accident risk, likely reflecting marijuana’s disruptive effects on motor coordination and time perception.

Impact on teenagers

Perhaps the biggest public health concern around medical marijuana liberalization and legalization concerns the potential impact on teenagers, who could have greater access to it as a drug of abuse and who may increasingly see marijuana as a “safe, natural” medicine rather than a harmful intoxicant. Although there is still much to learn about marijuana’s impact on the developing brain, the existing science paints a picture of lasting adverse consequences when the drug is used heavily prior to the completion of brain maturation in young adulthood. In teens, marijuana appears to impair cognitive development, may lower IQ and may precipitate psychosis in individuals with a genetic vulnerability.

Most states currently don’t allow medical marijuana for children, but they too are vulnerable. Accidental ingestion of marijuana edibles by children has increased in Colorado since marijuana was decriminalized for medicinal use in 2009. Also potentially concerning is the possibility of increased prenatal exposure if women self-treat with marijuana to control nausea associated with pregnancy. Research suggests prenatal exposure could have adverse consequences for children’s future health and brain development. There is as yet no research on the potential effects of secondhand marijuana smoke on children growing up in households where parents smoke.

Even in conditions for which THC, CBD or other cannabinoid constituents of the marijuana plant prove to be medically beneficial, consumption of the marijuana plant itself or its crude extracts via smoking, vaporizing or eating is unlikely to be the most effective, reliable or safe way for patients to obtain these benefits. Laboratory research is ongoing to better understand how cannabinoids work in the brain and body and hopefully guide development of safe, reliable therapeutic compounds that have a minimum of adverse side effects.

Existing medications

Two THC-based medications, dronabinol and nabilone, are already approved by the Food and Drug Administration to treat nausea caused by chemotherapy and to boost appetite in patients with AIDS wasting syndrome. The United Kingdom, Canada and several European countries have approved a drug called nabiximols (Sativex), containing THC and CBD, as a medication for spasticity caused by multiple sclerosis (MS) and, in Canada, for MS- and cancer-related pain. Despite its success in reducing pain and spasticity, it has not received approval in the United States, and recent evidence has found impairments in cognition in users.

CBD on its own is not psychoactive and it actually mitigates the “high” produced by THC; it has been studied as a potential antipsychotic drug, and ongoing trials are testing its efficacy as an antiseizure agent. Some parents of children with severe forms of pediatric epilepsy have claimed that high-CBD (and low-THC) marijuana extracts control their children’s seizures better than existing medicines. The maker of Sativex has recently created a CBD-based drug called Epidiolex to treat children with these conditions, and is in the process of conducting initial small-scale trials. Evidence so far shows that CBD is only effective in controlling seizures in a small subset of patients.

As public approval for medical marijuana grows, we need to ensure that our policy decisions are science-based and not swayed by the enthusiastic claims made widely in the media or on the Internet. We need to support and encourage increased research on marijuana’s potential benefits and conduct intensified research on the cannabinoid system to inform the development of safe, FDA-approvable drugs. But the existing science on marijuana’s adverse effects on youth demands we also proceed with caution in making policy changes that could result in increased use of or exposure to marijuana by young people.

Also see related Drugs & Health blog post on Medical Marijuana from our Teens site
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