Medical marijuana uses the marijuana plant or chemicals in it to treat diseases or conditions. The marijuana plant contains more than 100 different chemicals called cannabinoids. Each one has a different effect on the body. Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are the main chemicals used in medicine. THC also produces the "high" people feel when they smoke marijuana or eat foods containing it.
Each state that has legalized marijuana for medicinal use has different rules about what conditions qualify for treatment.
The active ingredients in cannabis are called cannabinoids. Each works by binding to receptors in the body’s endocannabinoid system. It’s as if this system was designed to respond effectively to cannabis. These are what provide the pain relief, stop the muscle spasms, calm the anxiety, etc.
To get medical marijuana, you need a written recommendation from a licensed doctor in states where that is legal. You must have a condition that qualifies for medical marijuana use. Each state has its own list of qualifying conditions. New York requires you to get a medical marijuana ID card. Once you have that card, you can buy medical marijuana at a dispensary.