Major research reviews point to a short list of potential benefits of cannabis, and they leave many popular claims unproven. The strongest evidence covers chronic pain in adults, nausea and vomiting from chemotherapy, and muscle spasticity reported by people with multiple sclerosis. For sleep, anxiety, PTSD and most other uses, the research is limited or mixed. Here's how researchers weigh that evidence, what the FDA has approved, the risks to consider and how to start the conversation with a clinician.
What cannabis is: cannabinoids, terpenes, THC and CBD
Cannabis contains many cannabinoids, plant compounds that act on the body's endocannabinoid system. The two best known are THC, which causes the high, and CBD, which doesn't. Terpenes give each strain its aroma. Our endocannabinoid system primer shows how these compounds interact with the body, and our CBD evidence guide looks at CBD on its own.
Research on medical marijuana uses covers two different things. Some studies test the plant itself or extracts made from it. Others test single-compound medicines: purified CBD, synthetic THC (dronabinol) or nabilone, a lab-made compound similar to THC. That distinction matters, because some of the strongest findings come from those medicines rather than from the flower or edibles you'd find in a dispensary.
How researchers grade the evidence
In 2017, a National Academies committee reviewed the research on cannabis and health and sorted its conclusions by strength:
| Level | What it means |
|---|---|
| Conclusive | Strong evidence from randomized controlled trials, with no credible opposing findings |
| Substantial | Strong evidence from several good-quality studies; a firm conclusion with minor limitations |
| Moderate | Some evidence from good- to fair-quality studies; a general conclusion with real limitations |
| Limited | Weak evidence; a conclusion is possible but uncertain |
| Insufficient | Mixed findings, a single poor study or no research at all |
Randomized controlled trials, where people are randomly assigned to cannabis or a placebo, carry the most weight. Surveys and observational studies can point to links, but they can't prove cause and effect. The committee also noted that federal regulations, including cannabis's classification as a Schedule I drug, made it hard to study. That's one reason so many questions remain open.
Where the evidence for the benefits of cannabis is strongest
The National Academies found conclusive or substantial evidence for three uses:
| Use | Form studied | Evidence level (2017) |
|---|---|---|
| Chronic pain in adults | Cannabis | Conclusive or substantial |
| Nausea and vomiting from chemotherapy | Oral cannabinoids | Conclusive or substantial |
| Multiple sclerosis spasticity, as reported by patients | Oral cannabinoids | Conclusive or substantial |
A newer review sharpens the picture for cannabis and chronic pain research. In 2026, Oregon Health & Science University researchers, funded by the federal Agency for Healthcare Research and Quality, pooled 25 short-term trials with 2,303 people. Most of them had nerve-related pain.
- Products with a comparable or high ratio of THC to CBD may bring small improvements. Compared with placebo, pain scores dropped by roughly half a point to three-quarters of a point on a 0-to-10 scale.
- Those gains came with more dizziness, sedation and nausea.
- Products low in THC and high in CBD may not improve pain.
- Among THC-only medicines, nabilone moderately reduced pain, while dronabinol did not.
Small, in other words, and not without trade-offs. Our article on cannabis and pain goes into the studies in more detail.
Where the evidence is limited or mixed
For many uses people ask about, the evidence is thinner. Here's what the 2017 review found:
- Sleep: moderate evidence of short-term improvement for people whose sleep is disrupted by sleep apnea, fibromyalgia, chronic pain or multiple sclerosis, mostly from nabiximols, a THC-and-CBD mouth spray.
- Anxiety: limited evidence that CBD eased anxiety during a public-speaking test in people with social anxiety disorder.
- PTSD: limited evidence, from one small trial of nabilone.
- Appetite and weight loss with HIV/AIDS, and Tourette syndrome: limited evidence.
- Dementia symptoms, glaucoma eye pressure, and depression symptoms in people with chronic pain or MS: limited evidence that cannabinoids are ineffective.
- Cancer, epilepsy, irritable bowel syndrome, ALS, Parkinson's disease and several other conditions: not enough evidence to say either way.
Limited evidence doesn't mean cannabis definitely fails for these uses. It means the studies so far are too few, too small or too mixed to rely on.
Research has moved since then in at least one area: the FDA has approved a purified CBD medicine for certain rare seizure disorders, covered below.
FDA-approved cannabinoid medicines
The FDA has approved four drug products built on three cannabinoids. Each is a prescription drug with a measured dose:
| Medicine | What it contains | Approved use |
|---|---|---|
| Epidiolex | Purified CBD | Seizures from certain rare conditions, including Lennox-Gastaut syndrome and Dravet syndrome |
| Marinol and Syndros | Dronabinol, a synthetic THC | Nausea from cancer chemotherapy; appetite loss with weight loss in AIDS |
| Cesamet | Nabilone, a synthetic compound similar to THC | Nausea from cancer chemotherapy |
The FDA has not approved a marketing application for cannabis itself for any disease or condition. Nabiximols, the mouth spray behind many of the sleep findings above, isn't on the list either. Dispensary products aren't FDA-reviewed medicines, even when they share an ingredient with one.
Product types and how delivery changes the experience
The way cannabis enters your body changes how fast it works and how long it lasts:
- Inhaled flower and vapes: effects usually begin within 10 minutes, peak within the first hour and fade in about three to four hours.
- Edibles, capsules and drinks: effects start 30 minutes to 2 hours after swallowing and may run as long as 12 hours. Drowsiness can linger into the next day.
- Tinctures held under the tongue: often thought to act faster than edibles, though studies are mixed.
- Topicals: creams and balms don't seem to cause a high, but their effectiveness hasn't been well established.
Clinical trials mostly test measured oral or mouth-spray doses, which are hard to match with dispensary products. The 2026 pain review even noted that it's unclear whether many of the studied products are available in the U.S.
Risks and side effects
An honest look at benefits has to include the downsides. The National Academies found substantial evidence linking cannabis use with:
- a higher risk of motor vehicle crashes
- schizophrenia and other psychoses, with the highest risk among the most frequent users
- worse breathing symptoms and more frequent chronic bronchitis with long-term smoking
- lower birth weight when cannabis is smoked during pregnancy
- a greater chance of problem cannabis use as use becomes more frequent
The committee also found moderate evidence that cannabis impairs learning, memory and attention while you're high. It found a similar level of evidence for a small increase in the risk of depression among people who use cannabis. In clinical trials, dizziness, sedation and nausea are common side effects. CBD can also change how some medicines work, including certain antidepressants and opioids, according to the Canadian Centre on Substance Use and Addiction.
Starting slowly, involving a clinician and Michigan medical card basics
If you're considering cannabis for a health reason, start with a conversation rather than a purchase.
- Talk with your clinician. Share what you hope to address, every medicine and supplement you take, and any heart, lung or mental health history. Ask whether a medicine the FDA has already approved fits your situation.
- Don't stop or change a medicine your doctor gave you without talking it through first.
- If you go ahead, start low and go slow. Use one product, the smallest amount, plenty of time between doses and notes on how you feel.
- Don't drive after using cannabis, and plan for hours of effects after an edible.
A few questions worth bringing to that appointment: What result would show it's working? Which side effects should make me stop? Could it interact with anything else I take?
Michigan medical card basics
Michigan's medical marijuana program is run by the state's Cannabis Regulatory Agency. Michigan residents 18 and older with a qualifying condition can sign up as patients after an evaluation by an active Michigan physician in the past six months. Those who don't designate a caregiver can apply online. Adults 21 and older can also buy cannabis without a card under Michigan's adult-use law.
Our step-by-step medical card walkthrough covers the application, and our patient guide covers what registered patients should know. To weigh whether a card is worth it for you, read our rundown of Michigan medical card benefits.
For any health question, your clinician is the right person to ask. 21+ only, or 18+ with a medical marijuana card. Please consume responsibly.
