Just The Facts
When a person smokes marijuana, THC quickly passes from the lungs into the bloodstream. The blood carries the chemical to the brain and other organs throughout the body. The body absorbs THC more slowly when the person eats or drinks it. In that case, the user generally feels the effects after 30 minutes to 1 hour.
THC acts on specific brain cell receptors that ordinarily react to natural THC-like chemicals in the brain. These natural chemicals play a role in normal brain development and function.
Marijuana over activates parts of the brain that contain the highest number of these receptors. This causes the "high" that users feel. In a placebo-controlled, 2007 study in the journal Neurology, Abrams and his colleagues found that marijuana is effective at reducing neuropathic pain, or pain caused by damaged nerves, in HIV patients. Opiates, such as morphine, aren't effective at treating that sort of pain. Researchers at the American Academy of Neurology have also found that medical marijuana in the form of pills or oral sprays seemed to reduce stiffness and muscle spasms in MS.