Cannabis-based medicines for chronic neuropathic pain in adults [Review] (2018)

Bottom line: There is a lack of good evidence that any cannabis-derived product works for any chronic neuropathic pain.
Background: Neuropathic pain is pain coming from damaged nerves. It is different from pain messages that are carried along healthy nerves from damaged tissue (for example, a fall, or cut, or arthritic knee). Neuropathic pain is treated by different medicines to those used for pain from damaged tissue.
Several products based on the cannabis plant have been suggested as treatment for pain, including neuropathic pain. These products include inhaled herbal cannabis, and various sprays or tablets containing active cannabis ingredients obtained from the plant, or made synthetically.
Some people with neuropathic pain claim that cannabis-based products are effective for them, and that is often highlighted in the media.
Study characteristics: In November 2017 we searched for clinical trials that used cannabis products to treat conditions with chronic neuropathic pain in adults. We found 16 studies involving 1750 people. Studies lasted 2 to 26 weeks. Studies compared different cannabis-based medicines. Ten studies compared an oromucosal (mouth) spray with a plant-derived combination of tetrahydrocannabinol (THC), the principal psychoactive constituent of cannabis, and cannabidiol (CBD), an anti-inflammatory ingredient of cannabis, against a fake medication (placebo). Two studies each compared inhaled herbal cannabis and cannabis plant-derived THC with placebo, and one study compared a man-made cannabinoid mimicking the effects of THC (nabilone) with placebo. One study compared nabilone with a pain killer (dihydrocodeine).
Key results and quality of the evidence:
We rated the quality of the evidence from studies using four levels: very low, low, moderate, or high. Very low-quality evidence means that we are very uncertain about the results. High-quality evidence means that we are very confident in the results.
There was no high-quality evidence.
All cannabis-based medicines pooled together were better than placebo for the outcomes substantial and moderate pain relief and global improvement. All cannabis-based medicines pooled together were better than placebo in reducing pain intensity, sleep problems and psychological distress (very low- to moderate-quality evidence).
There was no difference between all cannabis-based medicines pooled together and placebo in improving health-related quality of life, stopping the medication because it was not effective, and in the frequency of serious side effects (low-quality evidence).
More people reported sleepiness, dizziness and mental problems (e.g. confusion) with all cannabis-based medicines pooled together than with placebo (low-quality evidence). There was moderate-quality evidence that more people dropped out due to side effects with cannabis-based medicines than with placebo.
Herbal cannabis was not different from placebo in reducing pain and the number of people who dropped out due to side effects (very low-quality evidence).