Objectives:

The concern about the cannabinoid therapeutic group has been growing in recent decades, both at the level of publications and within the members of the Spanish Pain Society. The interest in cannabinoids in neuropathic pain (NP) is more recent, with the first publications dating back to 2001. This manuscript collects information from the presentation on NP and cannabinoids given for the Cannabinoids Interest Group Conference.

Material and methods:

A non-systematic narrative review was carried out. The search term was "medical cannabis" AND "neuropathic pain". The database used was PubMedâ Centralâ without date limits, with English search language. The most outstanding articles were selected from the categories: "meta-analyses and systematic reviews", "expert reviews" and "experience from others" (experiences in other countries, after approval).

Results:

Since 2001, 54 systematic reviews on cannabinoids and pain have been published with contradictory conclusions. An analysis of the reviews showed low quality of the clinical trials and of the reviews themselves. Of 10 specific reviews on cannabinoids and NP, the majority neither defined the objective of pain analyzed, nor the route of administration of the clinical trials analyzed, nor the type of agent analyzed. Only 1 met AMSTAR-2 high quality criteria while 7 were of critically low quality. A meta-analysis on the patient's impression of change opinion revealed an odds ratio of 2.0, (confidence interval 1.37-2.94). Some scientific societies have published recommendations on their use as 2nd or 3rd line therapies, but with considerable precautions and limitations. Contradictory data can also be observed in the experience of other countries. In Thailand the number of side effects increased significantly, especially with oil. In Israel, the intensity of pain decreased by 20 %, and the use of analgesics decreased by another 43 %. Morphine Equivalent Dose (DEM) decreased by 42 %. Disability improved by 19 %, and quality of life by another 25 %. Anxiety decreased by 40 % and depression by another 32 %, with an improvement in pain catastrophism of 17 %. In addition, patients reported a 33 % improvement in sleep disturbances, with a 14 % increase in sleep duration. However, in Denmark, users of tetrahydrocannabinol (THC) combined with cannabidiol, or pure THC used more daily doses of any analgesic (including opioids), but the consumption of NP-specific medications did decrease.

Conclusions:

Systematic reviews reach divergent conclusions about efficacy. The recommendations of the scientific associations differ for cannabis-based medicines and medical cannabis. This is because there are research gaps. Physicians who decide to use cannabis-based drugs or medical cannabis to treat DN should consider the limited robust evidence of effect and concerns about resulting harms.

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