Marijuana is gaining popularity in the United States as individual states have moved to make the drug legal. In fact, Connecticut was the most recent state to legalize the recreational use of marijuana. About 13% of U.S. adults use cannabis products. The plant has historically been used recreationally for its mind-altering effects, which can include enhanced senses and changes in mood. In some states, doctors can prescribe marijuana for medicinal uses such as reducing muscle spasms, pain, nausea, and vomiting.

But cannabis may have harmful long- and short-term effects, such as paranoia and memory loss, and it can be addictive and disrupt a user’s life and relationships.

Synthetic cannabinoids, compounds manufactured to replicate individual chemicals found in cannabis, are much more potent than cannabis and therefore could be more dangerous. Doctors at Yale Medicine treat patients for cannabis use disorder and are conducting leading research to advance therapies to treat it and to better understand the effects of cannabis on the brain.

Cannabis is a plant that contains compounds called cannabinoids. 

Some cannabinoids are psychoactive, meaning they act on the brain to modify mood or consciousness. Cannabis is usually smoked or vaporized and inhaled. It can also be consumed via tea, baked goods, candies, or other edible means.

Like the naturally occurring cannabinoids present in the cannabis plant, there are a number of synthetic cannabinoids that are made in a laboratory. Two synthetic cannabinoids are approved for use by the U.S. Food and Drug Administration to treat nausea and vomiting induced by chemotherapy, both available in capsule form. 

Other synthetic cannabinoids that are not legal have gained popularity in recent years. Those synthetics are often sprayed on dried plant materials for smoking and sold under the names “Spice” and “K2.” The synthetic cannabinoids generally have much stronger effects than cannabis.

Studies on the use of medical marijuana show evidence supporting its medicinal benefits. For example, it has been found to reduce muscle spasms associated with multiple sclerosis, and to reduce nausea and vomiting that often results from chemotherapy.

Immediate (acute) effects of cannabis, some positive and some negative, may include:

• Pain relief
• Stimulated appetite
• Reduced nausea and vomiting
• Reduced anxiety
• Rapid heart beat
• Low blood pressure
• Bloodshot eyes
• Slowed digestion
• Muscle relaxation
• Dry mouth
• Dizziness
• Hallucinations
• Paranoia

Limited data suggest that cannabis use is associated with motor vehicle accidents and can compound the risky effects of alcohol on driving.

About 10% of people who begin smoking cannabis will become addicted, and 30% of current users meet the criteria for addiction. 

People in mid-to-late adolescence are most likely to begin using cannabis. Some genetic studies suggest that developing cannabis addiction is hereditary. A Yale Medicine-led study identified several gene variants that increase risk of cannabis dependence. However, more research is needed in order to confirm the findings and understand how these genetic factors might contribute to marijuana dependence.

Regular or heavy use of cannabis can result in the development of tolerance and dependence. A person will need more and more marijuana to achieve the same effects. 

Adolescence, a period during which the brain is undergoing major changes, is an extremely poor time period for young people to try the effects of marijuana. Cannabis use in adolescence has been reported to increase the risk for schizophrenia.

Because cannabis is typically smoked, long-term use may harm the lungs. Marijuana also appears to be associated with deficits such as memory and attention problems.

For people trying to quit, withdrawal symptoms may include irritability, restlessness, difficulty sleeping, and hot flashes.

The American Psychiatric Association’s most recent criteria for substance use disorders include tools to identify cannabis addiction. For someone to be considered addicted, he or she must meet at least two of the 11 criteria, which include an inability to reduce consumption, constant cravings, and relationship and social problems. 

Behavioral therapies may help treat cannabis addiction. One approach, call motivational interviewing, helps to turn ambivalence about quitting into energy to quit. 

Contingency management gives patients tangible rewards for positive behaviors. 

Cognitive behavioral therapy, which helps to identify and modify damaging thinking and behavior, can also help people overcome addictions. 

Drugs that lessen marijuana cravings have often been unsuccessful. “There is an urgent need to develop effective treatments, either behavioral or pharmacological, for cannabis use disorder,” says Yale Medicine psychiatrist Deepak Cyril D’Souza, MD, a Yale Medicine psychiatrist. “It is likely that the combination of behavioral and pharmacological approaches will be superior to either alone."

Dr. D’Souza and others at Yale Medicine are hard at work developing the most promising behavioral, pharmacological, and combined treatments for cannabis use disorder.

Yale Medicine psychiatrists treat patients for all addictions, including cannabis use disorder. Yale Medicine doctors are conducting exciting research in the fields of marijuana and other addiction treatments. Preliminary results for clinical trials testing a drug that increases the brain’s cannabis-like proteins are promising — especially in terms of reducing drug use and withdrawal symptoms. 

Yale doctors have also conducted studies to measure the effects of combining psychotherapies to treat cannabis dependence.