The Mayo Clinic stated in its Aug. 25, 2006 article "Marijuana as Medicine: Consider the Pros and Cons," published on its website:

“When smoked or ingested, THC and other cannabinoids in marijuana attach to two types of receptors on cells in your body — like keys in a lock — affecting the cells, once attached.

CB1 is one such receptor. CB1 receptors are found mainly in your brain, especially in areas that control body movement, memory and vomiting. This helps explain why marijuana use affects balance and coordination and impairs short-term memory and learning, and why it can be useful in treating nausea, pain and loss of appetite.

The other type of receptor, CB2, is found in small numbers elsewhere in your body, mainly in tissue of the immune system, such as your spleen and lymph nodes. The function of these receptors is not well understood. They may serve as brakes on immune system function, which may help explain why marijuana suppresses your immune system.

After you smoke marijuana, its ingredients reach their peak levels in your body within minutes, and effects can last up to an hour and a half. When eaten — the plant is sometimes mixed with food — the ingredients can take several hours to reach their peak levels in your body, and their effects may last for hours.”

Aug. 25, 2006