In this study, scientists will evaluate the effectiveness of treating HIV-associated neuropathy with methadone alone and in combination with a novel cannabinoid SAB378. A cannabinoid is a molecule found only in the Cannabis plant. Cannabis and some cannabinoids are effective analgesics or pain relievers. The rationale for combination therapy is twofold: (1) medications with unique mechanisms of action may affect different aspects of neuropathic pain and (2) combination therapy may act synergistically—meaning the combined effect may be greater than the effect of each drug alone.