One of the longest-cultivated medicinal plants is marijuana, or Cannabis sativa, which is also used recreationally. For a long time, marijuana was completely illegal in most places, but in recent years, more and more attention has been paid to the medical aspects of the drug, and of the active ingredient tetrahydrocannabinol, or THC. As a result, a growing number of states and countries have changed their laws to allow marijuana to be bought, sold, prepared, and used medicinally. The most common uses of marijuana as medicine have been for chronic pain, eye pressure due to glaucoma, and multiple sclerosis, but it is also used as an anti-nausea drug to counteract the effects of chemotherapy, and for a wide range of other conditions, including Huntington’s disease, sleep disorders, and schizophrenia.
The medical uses of marijuana were described in Egyptian medical papyri nearly 4,000 years ago. Physicians employed it as a pain reliever, an anti-inflammatory drug, and for hemorrhoids. The Chinese word for cannabis is derived from elements meaning "big numbness"; an ancient Chinese physician who mixed powdered cannabis into wine is believed to be the first to use cannabis as an anesthetic. In India it was used for insomnia, labor pain, and gastrointestinal problems.
In modern times, an Irish doctor working in Kolkatta, discovering cannabis being used there, introduced it to the West through his experiments, first giving it to European patients for pain and stomach cramps, later experimenting with it more formally for migraines, sleeplessness, and pains. Until 1937, around the time laws against marijuana began to be passed in the United States, over 2,000 patent medicines containing marijuana were sold by more than 280 manufacturers.
Marijuana is renowned for being very safe, but it is not wholly without side effects. The general consensus is that there is almost no addiction potential, though some studies have found evidence that daily use can lead to addiction. However, the recreational effects of marijuana occur with medical use as well, where they are classified as side effect. Dizziness can occur, for example. Marijuana has effects on blood sugar levels, something diabetics should be aware of, and it can increase bleeding risk and lower blood pressure. However, these can generally be managed with a little planning.