In this crossover randomized controlled trial, 42 participants with spinal cord injury were randomized to receive vaporized cannabis containing placebo and 2.9% or 6.7% delta-9-THC during three 8-hour visits to determine if 6.7% THC was more effective for pain relief and determine the relationship of plasma cannabinoid levels and change in pain. The results from this study indicate that there was a significant decrease in burning and itching pain level measured by numeric rating pain scale of the patients receiving 6.7% THC. Adjusted relationship of plasma cannabinoid concentrations and change in pain level was not significant.