A recent report by the National Academies of Sciences, Engineering, and Medicine said there was definitive evidence that cannabis or cannabinoids (which are found in the marijuana plant) can be an effective treatment for chronic pain.
The report said that is "by far the most common" reason people request medical marijuana.
Last year, a large review from the National Academies of Sciences, Engineering, and Medicine assessed more than 10,000 scientific studies on the medical benefits and adverse effects of marijuana.
One area that the report looked closely at was the use of medical marijuana to treat chronic pain. Chronic pain is a leading cause of disability, affecting more than 25 million adults in the U.S.
The review found that marijuana, or products containing cannabinoids — which are the active ingredients in marijuana, or other compounds that act on the same receptors in the brain as marijuana — are effective at relieving chronic pain.
Alcoholism and drug addiction
Another comprehensive review of the evidence, published last year in the journal Clinical Psychology Review, revealed that using marijuana may help people with alcohol or opioid dependencies to fight their addictions.
But this finding may be contentious; the National Academies of Sciences review suggests that marijuana use actually drives increased risk for abusing, and becoming dependent on, other substances.
Also, the more that someone uses marijuana, the more likely they are to develop a problem with using marijuana. Individuals who began using the drug at a young age are also known to be at increased risk of developing a problem with marijuana use.
Depression, post-traumatic stress disorder, and social anxiety
The review published in Clinical Psychology Review assessed all published scientific literature that investigated the use of marijuana to treat symptoms of mental illness.
Evidence to date suggests that marijuana could help to treat some mental health conditions.
Its authors found some evidence supporting the use of marijuana to relieve depression and post-traumatic stress disorder symptoms.
That being said, they caution that marijuana is not an appropriate treatment for some other mental health conditions, such as bipolar disorder and psychosis.
The review indicates that there is some evidence to suggest that marijuana might alleviate symptoms of social anxiety, but again, this is contradicted by the National Academies of Sciences, Engineering, and Medicine review, which instead found that regular users of marijuana may actually be at increased risk of social anxiety.
Evidence suggests that oral cannabinoids are effective against nausea and vomiting caused by chemotherapy, and some small studies have found that smoked marijuana may also help to alleviate these symptoms.
Some studies on cancer cells suggest that cannabinoids may either slow down the growth of or kill some types of cancer. However, early studies that tested this hypothesis in humans revealed that although cannabinoids are a safe treatment, they are not effective at controlling or curing cancer.
The short-term use of oral cannabinoids may improve symptoms of spasticity among people with multiple sclerosis, but the positive effects have been found to be modest.
In June 2018, the Food and Drug Administration (FDA) approved the use of a medication containing cannabidiol (CBD) to treat two rare, severe, and specific types of epilepsy — called Lennox-Gastaut syndrome and Dravet syndrome — that are difficult to control with other types of medication. This CBD-based drug is known as Epidiolex.
CBD is one of many substances that occurs in cannabis. It is not psychoactive. The drug for treating these conditions involves a purified form of CBD. The approval was based on the findings of the research and clinical trials.
A study published in 2017 found that the use of CBD resulted in far fewer seizures among children with Dravet syndrome, compared with a placebo. Dravet syndrome seizures are prolonged, repetitive, and potentially lethal. In fact, 1 in 5 children with Dravet syndrome does not reach the age of 20 years.
In the study, 120 children and teenagers with Dravet syndrome, all of whom were aged between 2 and 18, were randomly assigned to receive an oral CBD solution or a placebo for 14 weeks, along with their usual medication.
The researchers found that the children who received the CBD solution went from having around 12 seizures per month to an average of six seizures per month. Three children receiving CBD did not experience any seizures at all.
Children who received the placebo also saw a reduction in seizures, but this was slight — their average number of seizures went down from 15 each month before the study to 14 seizures per month during the study.
The researchers say that this 39 percent reduction in seizure occurrence provides strong evidence that the compound can help people living with Dravet syndrome, and that their paper has the first rigorous scientific data to demonstrate this.
However, the study also found a high rate of side effects linked to CBD. More than 9 in 10 of the children treated with CBD experienced side effects — most commonly vomiting, fatigue, and fever.
The patient information leaflet for Epidiolex warns of side effects such as liver damage, sedation, and thoughts of suicide.