The intermediate doses yielded pain relief between the 0 percent THC placebo and the full-strength 9.4 percent dose. However, none were significantly effective compared with placebo.
Among the secondary effects, patients reported falling asleep more easily and more quickly with a greater feeling of drowsiness and less wakefulness while on 9.4 percent THC compared with placebo.
Mood and quality of life overall, though were unaffected.
Marijuana smoking appeared well tolerated, although the researchers noted that this may have been affected by the fact that most patients reported prior experience -- although not recent or extensive -- with the drug as an early ethics requirement to enter the study.
Patients rarely got high on the single hit they took through a pipe three times a day as part of the study, Ware's group noted.
None of the analgesic doses got plasma levels even halfway to the typical level seen among recreational users, they explained.
The most common drug-related adverse events associated with the most potent dose included headache, dry eyes, burning sensation in areas of neuropathic pain, dizziness, numbness and cough.
Collins cautioned that marijuana bought on the street, not through medical-use prescription, varies widely in potency, making the study results of unclear generalizability to the average user.