Hagenbach et al. (2007) performed a trial consisting of two open label phases; (I) dronabinol (oral THC) and (II) rectally delivered THC (followed by (III) double-blind, randomized, placebo control phase of oral dronabinol to evaluate efficacy and side effects for the treatment of SCI related spasticity. The main outcomes were the spasticity sum score (SSS) using the Modified Ashworth Scale as well as self-rating of spasticity. Due to numerous dropouts within the open label phases, the baseline SSS between groups were too large to perform the main analysis of phase III (dronabinol vs. placebo). In the open label phase, significant reductions in spasticity were seen in both oral and rectal THC groups. Analysis of dronabinol (phase I) versus placebo (phase III) was done instead: mean SSS decreased significantly on day 1 (p=0.001), day 8 (p=0.001) and day 43 (p=0.05). Self-rated spasticity decreased significantly on day 1 (p=0.033) but not day 8 or 43. There were no significant differences found with the remaining outcome measures. Due to the limitations in analysis, it remains unclear if placebo effects may have contributed to the positive findings in this study. We assign it a lower level of evidence (i.e., level 2) than would be expected of an RCT (i.e., PEDro≥6 = Level 1 RCT).
Pooyania et al. (2010) performed a double-blind, placebo-controlled, crossover trial of nabilone (0.5-1.0 mg/day) vs. placebo for 4 weeks for each treatment period with a 2-week washout period in between. They found a significant decrease in spasticity for those on active treatment (p=0.003) and overall muscles (p=0.001). There were no significant differences in other outcome measures. Contrary to Hagenbach et al. (2007), they reported only mild and tolerable side effects in this trial.
Wilsey et al. (2016) performed a crossover trial of placebo, 2.9% and 6.7% THC with a treatment time of 480 min. Participants took 4 puffs at t = 0 and 4 puffs at t = 240 min. They found a significant reduction of spasticity measured on a spasticity severity scale for 2.9% THC at t = 420 min. (p<0.0001) with significant spasticity relief (p=0.0277) but found no significant differences for the 6.7% THC group at any measurement points.
Kogel et al. (1995) performed a pre-post trial of dronabinol with dose escalation (2x5mg/day – 4×10 mg/day – 3x20mg/day) in five males with paraplegia. Two participants showed significant improvement in the pendulum test for spasticity, 1 showed fluctuating responses, 1 had no change and 1 had worsened.
There is level 1b evidence (from one RCT: Pooyania et al. 2010) that nabilone is effective in reducing spasticity in both the involved and overall muscles.
There is level 1b evidence (from one RCT: Wilsey et al. 2016) that 2.9% THC vapour is effective in reducing spasticity measured on a spasticity severity scale 420 min after 4 inhalations and 180 min after 4 additional inhalations.
There is level 2 evidence (from one compromised RCT: Hagenbach et al. 2007; supported by one pre-post study: Kogel et al. 1995) to support the use of oral delta-9-tetrahydrocannabinol (dronabinol) in reducing both objective and subjective measures of spasticity.