Phantom limb pain is a neuropathic condition affecting amputees. It occurs when damaged nerves at the site of the amputation continue to send signals to the brain, causing the amputee to think the missing body part is still there. Although phantom limb pain usually occurs after the amputation of an arm or leg, it can appear in any area of amputation, and discomfort can include not just pain but cold, heat, cramping, or any other common sensation.
It's estimated that phantom limb pain affects 50 to 80 percent of all amputees. The condition usually occurs during the first year after the amputation and often becomes chronic, lasting for months or even years with either no improvement or an increase in pain. Amputees may suffer from phantom limb pain their entire lives.
Veterans are one of the largest groups to experience amputations, with the wars in Iraq and Afghanistan alone resulting in 1,715 amputations as of January 2013. For them, and for other amputees, phantom limb pain can be devastating. Current treatment is a matter of trial and error, with little relief experienced by most patients. A 1984 survey of 5,000 U.S. amputee veterans found that 78 percent suffered from phantom limb syndrome, but a scant 1 percent experienced any relief through treatment.
In 2007, Health Canada approved Sativex, a whole-plant-derived cannabis extract, for the treatment of HIV-related neuropathic pain. While Sativex it is not currently available in the United States, it is in the process of FDA approval. Although not completely understood, the mechanism of action seems to be that cannabinoids work on specific pain receptors as well as the neurons that transmit pain.
In the United States, medical marijuana as a treatment for neuropathic pain has been the subject of much research. A 2007 study published in "Neurology" found that smoked cannabis reduced patients' pain by 30 percent over the course of only five days, and over three dozen preclinical and clinical trials have validated this finding. Cannabinoids act as a sort of circuit-breaker, binding to pain receptors and stopping the production of neurotransmitters which carry pain signals. They therefore provide some relief from chronic neuropathic pain, including the pain involved in phantom limb syndrome.