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What Medical Marijuana Works For

What studies say about cannabis' effect on chronic pain, MS, depression and other conditions

spinner image A banner that reads Marijuana and Your Health with an image of a scientific glass beaker containing a marijuana stalk with leaf and a vial of t h c oil
spinner image Patients placing orders at a medical marijuana dispensary
Patients place orders for medical marijuana at a dispensary in Florida.
Paul Hennessy/NurPhoto via Getty Images

Evaluating medical marijuana research disease by disease is not easy, hampered as it is by the federal government’s ban on government-supported data collection. Observational studies — in which users simply report their experiences — may look rosy. Animal and test-tube studies also can sound promising. But plenty of stuff that helps mice or a clump of cells in a petri dish may not help us humans. Despite these obstacles, there are some conditions and diseases for which cannabis is clearly a useful treatment. Others, not so much.

Chronic pain

More than 600,000 Americans turn to cannabis for relief from chronic pain — and the scientific evidence for its effectiveness is substantial. In gold-standard randomized clinical trials of people who had agonizing health concerns — peripheral neuropathy (nerve pain from diabetes), spinal cord injury, HIV or complex regional pain syndrome, cancer, chemotherapy, muscle and joint problems, rheumatoid arthritis and multiple sclerosis — cannabis reduced pain by 40 percent, according to the 2017 NASEM report.

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In a recent Canadian study, cannabis even soothed arthritic lab rats. Surprisingly, there’s little evidence (yet) from human studies for the most common form of arthritis, osteoarthritis — the wear-and-tear joint disease affecting 50 percent of adults age 65-plus. Clinical trials are underway. But who’s waiting? Arthritis was the top reason older adults used cannabis in a 2019 Colorado survey, followed by back pain. Overall, 79 percent said it helped. 

BOTTOM LINE: It seems to help


The National Academies rate scientific proof for better sleep on cannabis as only “moderate” in people with health conditions that interfere with slumber. But that’s not slowing down older users. More than 1 in 3 people in a Colorado survey tried it for sleep; 86 percent said it helped. By plugging into cannabinoid receptors on brain cells, THC and CBD could possibly team up for better sleep, at least in the short term, in people with insomnia due to pain, obstructive sleep apnea, fibromyalgia, multiple sclerosis and anxiety.

But beware: Choosing cannabis for sleep can be tricky. A little THC helps, but too much could keep you awake. Too little CBD could interfere with good sleep, while a bigger dose may help you snooze longer with fewer overnight wake-ups, a recent Palo Alto University review says.

BOTTOM LINE: It seems to help

Depression, anxiety and PTSD

Lifting low moods and calming chronic tension brought 1 in 5 older adults in a recent survey to medical cannabis. More than 90 percent said it helped. Meanwhile, treatment of post-traumatic stress disorder (PTSD) is emerging as another top use.

So far, data for all of these mental health issues is sparse. We’ll know more soon. At least seven studies of cannabis in anxiety and/or depression are in the works in the United States and around the world. So are at least six studies for PTSD. 

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For now, small studies and surveys hint at benefits and problems — especially for depression. The good news: In a 2018 Washington State University online survey of 3,151 medical marijuana users with depression, in-the-moment symptoms improved by 50 percent after just two puffs of generally low-THC, high-CBD pot. As with any drug, dosage matters: More wasn’t better. The bad news: Over time, their ongoing depression worsened somewhat. Regular use may change cannabinoid receptors in the brain, boosting vulnerability to dark moods, the researchers note. Stopping can reverse it.

Note: Potency varies by strain and form, and it can often be tough to gauge a patient's tolerance. So before a patient engages in a cannabis-based medical treatment, he or she should consult their doctor and approach with caution; there’s limited scientific research and, as with any medication, the effects vary by user.

The picture looks brighter for anxiety — if you choose your cannabis carefully. In a 2018 study, volunteers who used cannabis reduced their use of commonly prescribed anxiety-reducing benzodiazepines by 47 percent. Users are enthusiastic. “Anxiety can really increase as you get older,” notes Barbara Blaser, 73, a nurse navigator who helps teach older cannabis users at Magnolia Wellness dispensary in Oakland, California. “Your kids are far away, your friends are passing away, you don’t know what will happen next in your life. A small amount of cannabis can help you feel better. Right now, I’m using a gel pen that delivers a tiny dab to my skin. It sinks in and I relax.” 

Quantity matters: A little bit (7.5 milligrams of THC, less than the content of many edibles) reduced stress in a 2017 study. But 12.5 milligrams (what you’d get from a few puffs of the popular pot strain GSC (formerly Girl Scout Cookies) increased anxiety.

Cannabis has potential for people with PTSD. THC and CBD may soften “fear memories” that flood the brain in response to PTSD triggers (such as a sudden loud noise), say researchers from the National Center for PTSD in Palo Alto, California. Taking THC at night meant fewer and less intense nightmares for 47 people with PTSD in a 2009 clinical trial in Canada. 

BOTTOM LINE: Depression — mixed success; anxiety — seems to help; PTSD — seems to help

Multiple sclerosis

Nearly 1 million Americans, including many 45 and older, live with the debilitating muscle spasms and pain of multiple sclerosis. Up to 66 percent of them may be using medical marijuana, a 2017 survey found. It’s likely they’ve cut back on MS medications, too. In fact, people with MS are the second-largest group of medical marijuana users in the U.S., behind chronic pain sufferers. There’s substantial science for cannabis’ ability to reduce MS muscle spasms. Meanwhile, others are looking at a potential cannabis-based drug for MS. The cannabis research and development company MMJ International Holdings Corp. hopes to test an experimental medication — a highly purified, liquid plant extract with THC and CBD in a gelatin capsule — for MS in the U.S. soon.   

BOTTOM LINE: It seems to help

Cancer pain

Cannabis is highly effective for cancer pain and the side effects of cancer treatment — nausea, vomiting, loss of appetite and weight loss, says Donald Abrams, an oncologist and professor of medicine at the University of California San Francisco and a longtime advocate of medical marijuana. “There’s no question in my mind, it works,” Abrams says. “I was on the NASEM committee that reviewed the evidence.”

The uses with the strongest evidence in the medical literature were for nausea and vomiting caused by chemotherapy and cancer pain. “I work with patients undergoing cancer therapy,” Abrams says. “I tell them, ‘Go to the dispensary, tell them what you’re trying to treat, and ask what works best.’ ” 

But cannabis should never be used to treat cancer, Abrams says. “The saddest and most frustrating thing for me is to meet patients who’ve delayed coming in for six months because they heard marijuana treats cancer and they wanted to try it first. For some, it’s too late for proven treatments like surgery, chemotherapy and radiation that extend and save lives.” Don’t fall for hints online that it does work, he notes — they’re based on sketchy anecdotes and questionable research, like one tiny human study that dripped cannabis into the brains of people with brain cancer.

BOTTOM LINE: It seems to help

Other conditions

Older adults are using medical marijuana for dozens of other health concerns, including migraines, fibromyalgia, symptoms of Alzheimer’s disease and dementia, Parkinson’s disease, Crohn’s disease and glaucoma. Some show promise. Medical marijuana reduced the frequency and intensity of migraines in one study. A study of 2,700 older patients in Israel gave cannabis high marks for reducing pain and improving quality of life for those with Alzheimer’s, Parkinson’s, Crohn’s and ulcerative colitis. Meanwhile, experts say that when it comes to glaucoma, do not rely on marijuana. It’s important to stick with proven treatments like eye drops. Far more research and anecdotal weight is needed before there are definitive answers on these uses.

BOTTOM LINE: Mixed results  

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