There has long been a belief that cannabis provides an analgesic quality to those suffering from chronic pain. Those suffering from neuropathic pain - commonly caused by alcoholism, amputation, spine surgery, HIV or MS - often turn to medicinal cannabis as a source of relief.
In a 2010 study done by the Canadian Medical Association Journal, 21 men and women, average age 45, were tested with four different strengths of cannabis - one at 9.4% THC, one at 2.5% THC, the other 6% THC and one placebo [source: Doheny, Kathleen]. Over the course of two months, each test subject smoked a random strain (they had no knowledge of the different strengths) three times a day for five days. After the five-day period, the subjects rated their level of pain. The highest dosage of THC (9.4%) was shown to lower the pain level from 6.1 to 5.4 on average. Though a small change, the study notes that most strains sold on the street are at 10% or 15% THC levels and therefore may produce an even lower pain rating [source: Doheny, Kathleen].