This study involved individuals with various chronic pain states, including musculoskeletal pain from osteoarthritis and other causes, neuropathic pain, sickle cell disease, and others. These patients were already using long-acting opioids: either time-released oxycodone twice daily at mean doses of 100 mg/day or time-released morphine twice daily at mean doses of about 120 mg/ day. More than 300 individuals were screened, and ultimately 21 of these participated in the study. Participants had to be stable on their opioid regimens before they were enrolled.

The 21 participants were managed as inpatients over 5 days. On the first day, they received 1 evening dose of vaporized cannabis; on days 2-4, they received 3 doses; and on day 5, they received a morning dose, in addition to their typical opioid regimens.

On average, these participants experienced an added 27% reduction in pain with the addition of vaporized cannabis. Pharmacokinetic studies demonstrated that although there was an effect on reducing absorption of morphine by the addition of vaporized cannabis, there was no change in the area under the curve. Therefore, the patients were exposed to a similar amount of morphine, although the peak concentration of morphine was also slightly reduced. Adding vaporized cannabis seemed to independently magnify the response the person was experiencing to the analgesia.