Cannabis and Health: Where the Evidence Supports Benefits, and Where It Does Not

Cannabis and its compounds, including tetrahydrocannabinol (THC) and cannabidiol (CBD), are being studied for a range of medical uses. But the evidence is uneven: some cannabinoid medicines have established roles, while many popular claims remain preliminary, overstated or unsupported in human studies.

A useful starting point is the National Academies’ 2017 review of cannabis and cannabinoid research, which examined evidence on potential therapeutic effects as well as health risks. Its conclusions point to several areas of promise—but not to cannabis as a general treatment for physical or mental well-being.

1. Anxiety: possible benefit, but not a general treatment

CBD may reduce anxiety in some circumstances. However, human evidence remains limited, and a small study of people with social anxiety disorder does not establish that over-the-counter CBD products treat anxiety disorders broadly. THC can produce relaxation for some people but may also trigger anxiety, paranoia or impaired judgment, particularly at higher doses.

People with persistent anxiety should not substitute cannabis for evidence-based treatments without discussing the decision with a qualified clinician.

2. Inflammation and pain: modest evidence for some chronic pain

Cannabinoids affect receptors involved in pain and immune signaling, which has prompted research into their possible anti-inflammatory effects. In clinical studies, however, the clearest evidence concerns modest short-term reductions in some forms of chronic pain—not a proven ability to reduce inflammation throughout the body.

The National Center for Complementary and Integrative Health reports that some cannabis-based medicines may help chronic or neuropathic pain, but the benefit is generally small and side effects such as dizziness, sleepiness and cognitive impairment are more common than with placebo.

3. Blood pressure: cannabis is not a proven cardiovascular therapy

The claim that cannabis lowers blood pressure and protects against heart attack or stroke is misleading. Cannabis can make the heart beat faster and raise blood pressure immediately after use. It may also affect the cardiovascular system in ways that increase concern about stroke and heart disease, although the long-term risks and the effects of different products and methods of use are still being studied.

The Centers for Disease Control and Prevention’s review of cannabis and heart health does not describe cannabis as a treatment for hypertension or a way to prevent cardiovascular disease.

4. Cancer: laboratory findings are not cancer treatment

Cannabinoids have caused cancer cells to die or grow more slowly in some laboratory and animal experiments. Those findings may help guide future research, but they do not show that cannabis cures cancer or slows cancer progression in people.

The National Cancer Institute states that the U.S. Food and Drug Administration has not approved cannabis or cannabinoids as a cancer treatment. Certain prescription cannabinoid medicines may help with chemotherapy-related nausea and vomiting, but that is symptom management rather than an anticancer effect. Patients should not delay conventional cancer care in favor of cannabis products.

5. Addiction and relapse: no reliable evidence of prevention

There is not good evidence that regular cannabis use prevents relapse from alcohol or other substance-use disorders. Some people report using cannabis to manage cravings, anxiety or insomnia, but those observations do not establish that it is an effective treatment. Cannabis can also become problematic: the CDC estimates that roughly three in 10 people who use cannabis may develop cannabis use disorder, with risk affected by factors such as age at first use and frequency of use.

Treatment for addiction should be guided by an addiction specialist or other qualified health professional. Cannabis should not be presented as a broadly effective relapse-prevention medicine.

6. Gastrointestinal disorders: symptom relief is different from treating disease

People with Crohn’s disease, ulcerative colitis and other gastrointestinal conditions sometimes use cannabis for abdominal pain, nausea, poor appetite or diarrhea. Small studies and reviews suggest that some patients may experience improved symptoms or quality of life.

That does not mean cannabis treats the underlying intestinal inflammation. A systematic review of inflammatory bowel disease research found that cannabinoids did not induce remission or improve inflammatory biomarkers, even when some patient-reported symptoms improved. Cannabis should therefore not replace prescribed therapies that control inflammation and prevent complications.

7. Sleep: short-term effects remain uncertain

Cannabis may make some people feel sleepy or may improve sleep when pain or another illness is keeping them awake. Research has often found better self-reported sleep among people using cannabinoid products, but it is unclear whether cannabis improves sleep directly or simply reduces symptoms of another condition.

Evidence for treating insomnia in otherwise healthy adults remains limited. THC can impair memory and alertness, and regular use may lead to tolerance, dependence or withdrawal-related sleep problems. Claims about cannabinol, or CBN, as a reliable sleep aid are also not supported by strong clinical evidence.

8. Approved cannabinoid medicines: a narrower category

It is important to distinguish cannabis products sold in dispensaries or online from standardized prescription medicines. The FDA has approved Epidiolex, a purified CBD medicine, for seizures associated with Lennox-Gastaut syndrome, Dravet syndrome and tuberous sclerosis complex. It has also approved prescription drugs containing synthetic THC for specific uses, including chemotherapy-related nausea and appetite loss associated with HIV/AIDS.

Those approvals apply to particular products, doses and medical conditions. They do not establish that unregulated CBD oils, edible products or smoked cannabis are safe or effective treatments for the many conditions discussed above. CBD can cause liver injury, interact with other medicines and produce significant drowsiness; THC can impair coordination, memory and reaction time.

Cannabis may have a role in managing selected symptoms and conditions, but its benefits depend on the cannabinoid, dose, formulation, route of administration and patient. Anyone considering cannabis for a medical problem should discuss it with a doctor or pharmacist—especially people who are pregnant or breastfeeding, have heart or psychiatric conditions, take other medications, or are being treated for cancer.