Phantom limb pain (PLP) is a debilitating condition experienced by up to 85% of amputees. A complex mixture of central and peripheral pain, PLP is often resistant to conventional analgesics. Despite the success of marijuana in treating neuropathic pain and a strong mechanistic rationale, there are limited studies addressing its effectiveness in the management of PLP. 

A 70-year-old male presented to the neurology clinic with a 32-year history of PLP following transfemoral amputation of his left leg. His pain was refractory to multiple therapies, including opioids, and significantly impaired quality of life and independence. The patient was prescribed medical marijuana pills starting at a 20:1 CBD:THC ratio under mixed guidance with a pharmacist. He was interviewed at two and four month intervals after beginning treatment.

During his first two months of treatment, the patient experienced a 40% reduction in pain, better sleep quality, and marked improvement in quality of life. During the third month, however, the patient’s PLP worsened and ingestion of marijuana during episodes became associated with a paradoxical increase in pain. After progressive alteration of the CBD:THC ratio to 1:1 produced progressive exacerbations of pain, the patient stopped taking marijuana and his pain during episodes returned to baseline.

This case is, to our knowledge, the first to demonstrate initial success and subsequent rebound pain in a patient taking medical marijuana for PLP. While the source of the patient's rebound pain is unclear, a mechanism for marijuana-induced hyperalgesia involving dorsal horn sensitization has been demonstrated, suggesting that dorsal horn changes occurring after amputation may have played a role. Further trials of marijuana in PLP are necessary to explore its therapeutic effects and potential complications. Given the high prevalence of amputation among veterans, the federal injunction against medical marijuana in Veterans Administration hospitals poses significant challenges to further research.