Medical marijuana is cannabis that a doctor recommends to treat or manage symptoms of a specific health condition. The plant contains over 100 active compounds called cannabinoids, but the two that matter most are THC and CBD. THC is the compound responsible for the “high” associated with marijuana, while CBD does not produce that mental effect. Medical marijuana programs exist in most U.S. states, though cannabis remains a Schedule I controlled substance at the federal level.
How Cannabinoids Work in Your Body
Your body has its own built-in system for responding to cannabinoids, called the endocannabinoid system. It includes two main types of receptors. The first type, found primarily in the brain, outnumbers many other receptor types there. These receptors act like traffic cops, controlling the levels and activity of other chemical messengers. They regulate things through immediate feedback, turning up or down whichever system needs adjusting, whether that’s hunger, temperature, or alertness.
The second type of receptor exists mostly in immune tissues. It helps control immune function and plays a role in managing intestinal inflammation, contraction, and pain in inflammatory bowel conditions. When you use medical marijuana, the cannabinoids from the plant interact with these same receptors, which is why cannabis can affect such a wide range of symptoms, from pain and nausea to muscle spasms and seizures.
Conditions It’s Used For
Each state maintains its own list of qualifying conditions, but there is significant overlap. The most common include chronic or severe pain (especially nerve-related pain), epilepsy and intractable seizures, multiple sclerosis, cancer (including symptom management during remission therapy), Crohn’s disease, inflammatory bowel disease, HIV/AIDS, Parkinson’s disease, and PTSD. Many states also include ALS, Huntington’s disease, glaucoma, anxiety disorders, autism, sickle cell anemia, Tourette syndrome, and terminal illness.
Some states are expanding their lists through research programs. Pennsylvania, for example, has added moderate to severe traumatic brain injury and type 2 diabetes as approved conditions specifically for research purposes. The trend across the country has been toward broader qualifying criteria, with a few states allowing doctors to recommend cannabis for any condition they believe it will help.
FDA-Approved Cannabis Medications
While most medical marijuana is purchased as a whole-plant product from a dispensary, the FDA has approved a small number of cannabis-related medications that work through the traditional pharmacy system. Epidiolex contains a purified form of CBD and is approved to treat seizures associated with Lennox-Gastaut syndrome, Dravet syndrome, and tuberous sclerosis complex in patients one year and older. It was the first plant-derived cannabis medication to receive FDA approval.
Two other approved drugs, Marinol and Syndros, contain a synthetic version of THC. They’re used to treat severe weight loss in AIDS patients and nausea from chemotherapy. A similar synthetic, sold as Cesamet, has a chemical structure close to THC and serves comparable purposes. These medications are prescribed and dispensed like any other pharmaceutical, separate from state medical marijuana programs.
Ways to Use Medical Marijuana
The method you choose affects how quickly cannabis takes effect and how long it lasts.
- Inhalation (smoking or vaporizing): Effects begin within minutes and last 2 to 4 hours. This is the fastest route, which makes it easier to control dosing in real time.
- Edibles (capsules, gummies, baked goods): Takes longer to kick in because the cannabinoids must pass through your digestive system, but effects last 6 to 8 hours. The delayed onset makes it easier to accidentally take too much.
- Sublingual (tinctures or sprays held under the tongue): Onset ranges from 15 to 45 minutes, with effects lasting 6 to 8 hours. This method avoids the lungs while still absorbing faster than edibles.
- Topicals (creams, balms, patches): Applied directly to the skin for localized relief. Onset and duration vary widely depending on the product and the area treated.
Side Effects and Risks
Most side effects come from THC rather than CBD. Common ones include headaches, dry mouth, red and dry eyes, fatigue, coughing, and wheezing (particularly with inhaled forms). At higher THC doses, side effects can escalate to nausea, vomiting, anxiety, memory problems, and in some cases hallucinations or psychosis.
Certain groups face higher risks. People who are pregnant may experience changes in heart rate or blood pressure, and cannabis use during pregnancy is linked to premature birth and low birth weight. Those with active heart disease, active mental health disorders, or a history of substance misuse should avoid using cannabis. Interestingly, while glaucoma appears on many qualifying condition lists, some research shows cannabis can lower blood flow to the optic nerve, which could actually worsen vision in people with that condition.
How to Get a Medical Marijuana Card
The process varies by state but follows a general pattern. First, you visit a physician who is certified to recommend medical marijuana. This can be an in-person or telemedicine appointment in most states. The doctor evaluates whether you have a qualifying condition and, if so, enters a recommendation into your state’s patient registry. You’ll need a valid state-issued ID, such as a driver’s license.
After the doctor submits their recommendation, you typically receive an email or notification to complete your registration online. You’ll review your personal details, accept a legal statement, and receive a registry card (physical or digital). With an active card and recommendation, you can purchase cannabis products from a licensed dispensary in your state. Most states require you to renew your registration annually, which includes at least one doctor visit per year.
Federal vs. State Law
Cannabis is classified as a Schedule I controlled substance under the federal Controlled Substances Act, the same category as heroin. This classification means the federal government considers it to have no currently accepted medical use and a high potential for abuse. There has been ongoing discussion about rescheduling marijuana to Schedule III, which would place it alongside drugs like testosterone and ketamine, but as of now, no reclassification has taken effect.
This federal-state conflict creates real complications. You cannot legally carry medical marijuana across state lines, even between two states where it’s legal. Veterans using VA healthcare cannot be prescribed cannabis through federal facilities. Banks have historically been reluctant to serve cannabis businesses. For patients, the practical takeaway is that your medical marijuana card is only valid within the state that issued it, though a handful of states offer reciprocity agreements that honor out-of-state cards.