As a medicine, cannabis may just be a wonder plant. Ancient cultures dating back to 500 BC grew marijuana plants and utilized their medicinal capabilities to treat everything from minor discomfort to deadly disease.

There’s nothing new about the medicinal use of marijuana, but thanks to prohibition, the modern era refused to openly acknowledge its power until 1996: That’s when California voters passed the first medicinal cannabis law. Several other states followed suit, and by 2020, 36 states and 4 territories allowed some form of MMJ.

Which compounds in cannabis treat disease?

Marijuana contains a host of important compounds known as cannabinoids. These substances mimic similar cannabinoids produced by the human body, and they influence a wide range of mental and physical processes, including appetite, pain sensitivity, and mood. The most critical chemicals found in cannabis are THC and CBD.

THC. THC, or tetrahydrocannabinol, is the cannabinoid that gets marijuana users high. The more THC a sample of cannabis contains, the more intoxicating it is likely to be for the people who smoke it. This is the chemical most sought after by recreational users, but it also serves many medical purposes.

CBD. CBD, by comparison, is non-intoxicating but also has a wide range of medicinal uses. Formally known as cannabidiol, CBD is used primarily to treat children with intractable seizure disorders, but it can also help with multiple sclerosis, cancer, and other conditions. This cannabinoid is especially popular in deep-red states, where it can be used as medicine without causing the high that motivates many conservatives to oppose marijuana reform.

Common medical marijuana qualifying conditions

So, how can cannabis help? Here are just some of its many uses.


Marijuana can be used to treat the chronic pain and inflammation associated with rheumatoid arthritis, osteoarthritis, and psoriatic arthritis, as well as other conditions involving arthritic joints.


Cachexia is a form of chronic wasting caused by cancer, its treatments, and a number of other medical problems. Cannabis can effectively boost appetite, allowing patients with this condition to reach and maintain a healthy weight.


Marijuana is also used to treat cancer on two fronts. First, it alleviates the nausea, vomiting and pain caused by chemotherapy and radiation treatment. Second, it may actually fight cancer cells, preventing and even shrinking tumors.

Crohn’s Disease

Crohn’s Disease is a chronic inflammatory bowel disease that causes discomfort, pain, and digestive problems. The ulcers and pain associated with this gastrointestinal disorder condition can be disabling, but marijuana has shown great promise in relieving the worst of the symptoms.

Researchers have established that marijuana is effective in improving appetite, fighting insomnia, and even sending Crohn’s into remission.

Chronic Pain

A growing body of science shows that marijuana is effective in alleviating chronic pain, though these conclusions remain controversial. This is the most common reason patients seek medical cannabis. States have been slow to add chronic pain to their lists of qualifying conditions, but the science behind pot as a painkiller is growing stronger.


Marijuana may also be helpful in treating and even preventing Alzheimer’s disease and other types of dementia. Scientists believe Alzheimer’s is caused by cellular inflammation in the brain. Weed, which is an effective anti-inflammatory, may ward off that inflammation and help prevent dementia.


Diabetics can benefit from medical cannabis, as well. Regular use of the drug leads to lower insulin levels, lower insulin resistance, and slimmer waistlines, all good news for patients who have Type 2 diabetes or are at risk of developing it.


In the United States, marijuana was first used primarily to treat glaucoma, a condition that involves excessive blood pressure in the eyes. Cannabis reduces that pressure and helps prevent further damage to the retina. Cannabis was also recommended for nausea by at least as early as the 1970s.


Cannabis is used to treat a host of symptoms caused by HIV and AIDS, including loss of appetite, cachexia or wasting syndrome, pain, and nausea, as well as depression and other emotional issues.

HIV is much more survivable than it used to be. In the early years of the AIDS crisis, a diagnosis was a death sentence. Now, patients routinely live full lives on a complex regimen of medications, including cannabis.


Migraine headaches, a common and sometimes debilitating condition, can be treated with marijuana, which is used primarily to relieve the intense pain that accompanies them.

Muscle Spasms

MS is a progressive, neurodegenerative disease, and though there is no cure, cannabis is one of several medications that can make a critical difference in reducing symptoms. The drug helps ease the pain and muscle spasms that define the disorder, and is covered by MMJ in most states that allow the drug.

Severe Nausea

One of the first medical uses of marijuana was as a treatment for the severe nausea caused by cancer and its treatments. It can also effectively relieve other forms of nausea, including those caused by AIDS and chronic digestive disorders.

Seizures and Epilepsy

Much of the recent attention to medical marijuana has focused on its success in treating severe epilepsy. Cannabidiol (or CBD), one of the constituent chemicals of cannabis, effectively reduces brain activity that causes convulsions, especially in children. This discovery has greatly increased support for medical marijuana programs.

Tourette’s Syndrome

Several mental illnesses are thought to respond to MMJ, including anxiety, mood disorders, and obsessive-compulsive disorder. But the drug is particularly helpful in treating Tourette’s syndrome, a neuropsychiatric disease typified by physical tics and obsessive-compulsive behaviors. Repeated studies have shown weed can reduce these symptoms without serious adverse effects.

The data on mental illness is still a little unsettled, but many sources suggest pot can reduce the symptoms of anxiety, mood disorders, and ADHD. Evidence is limited on this front, with some suggesting cannabis may actually harm some patients with serious mental illnesses.

States where medical marijuana is legal

As of 2020, 36 states and 4 territories have comprehensive, state-regulated medical marijuana programs in place. California was the first to legalize medicinal cannabis, with the Compassionate Use Act of 1996.

A majority of these states allow so-called “whole-plant” medical marijuana, which can include noticeable levels of the intoxicating chemical THC. The others restrict medicinal use to plant matter containing only CBD, a non-intoxicating chemical used to treat seizures and a shortlist of other conditions.

The states which allow whole-plant medicinal cannabis, including THC, are shown in the table below, along with the associated possession limits.

Possession Limit
1. Alaska
1 oz usable; 6 plants (3 mature)
2. Arizona
2.5 oz usable; 12 plants
3. Arkansas
2.5 oz per 14-day period; no plants
4. California
8 oz; 12 plants (6 mature)
5. Colorado
2 oz usable; 6 plants (3 mature)
6. Connecticut
2.5 oz; no plants
7. Delaware
6 oz; no plants
8 .D.C.
2 oz; no plants
9. Florida
4 oz; no plants
10. Hawaii
4 oz usable; 7 plants
11. Illinois
2.5 oz; 5 mature plants
12. Louisiana
30-day supply of non-smokable; no plants
13. Maine
2.5 oz; 6 mature plants
14. Maryland
30-day supply, no edibles; no plants
15. Massachusetts
10 oz; limited cultivation
16. Michigan
2.5 oz; 12 plants
17. Minnesota
30-day supply of non-smokable marijuana; no plants
18. Mississippi
2.5 oz; no plants
19. Missouri
8 oz; 6 mature plants
20. Montana
1 oz usable; 8 plants (4 mature)
21. Nevada
2.5 oz; 12 plants
22. New Hampshire
2 oz; no plants
23. New Jersey
3 oz per month; no plants
24. New Mexico
8 oz; 16 plants (4 mature)
25. New York
30-day supply non-smokable marijuana; no plants
26. North Dakota
3 oz; no plants
27. Ohio
90-day supply, per recommendation; no plants
28. Oklahoma
8 oz; 12 plants (6 mature, 6 immature)
29. Oregon
24 oz usable; 24 plants (6 mature, 18 immature)
30. Pennsylvania
30-day supply; no plants
31. Rhode Island
2.5 oz; 24 plants (12 mature)
32. South Dakota
3 oz; 3 plants
33. Utah
30-day supply not to exceed 113 grams; no plants
34. Vermont
2 oz usable; 9 plants (2 mature)
35. Virginia
90-day supply; no plants
36. Washington
3 oz usable; 6 plants
37. West Virginia
30-day supply (amount TBD); no plants

Medical marijuana cultivation laws

At least 20 states allow the cultivation of marijuana as medicine, including the 15 where the drug is legal for any use. The District of Columbia also allows home grows for medical use. But, these laws often change due to court rulings and new legislation, so public information about them may not be up to date.

As a general rule, states with whole-plant medical marijuana legalization allow patients to cultivate, while those with low THC or “CBD-only” laws do not. A few states have decriminalized small grows without legalizing medicinal marijuana. Visit our Cultivation Laws page for a state-by-state breakdown.

How to become a medical marijuana patient

Each state has its own process of becoming a medical marijuana patient. Most require formal registration with the state’s department of health, while California mandates only a piece of paper from a doctor.

To obtain your medical marijuana patient card through your state’s Department of Health Services, a physician must validate a qualifying medical condition during an exam and fill out the required documentation. Then, you can apply for a medical marijuana card. The application process is typically a series of forms that can be completed online through the state’s site. The approval process can take weeks, and once approved you will receive access to an online portal that supports your experience as a patient.

Your rights as a medical marijuana patient vary based on your home state. Check out your state laws for medical marijuana here.

Follow the full legalization of medical marijuana on our timeline.