Key messages
Due to a lack of robust evidence, the benefits and harms of cannabis-based medicines are unclear.
Larger, well-designed studies including people with serious internal diseases (e.g. heart, kidney) and mental disorders are needed to give better estimates of the benefits and harms of cannabis-based medicines.
Introduction to the review topic
What is neuropathic pain?
Neuropathic pain is nerve pain coming from malfunctions of or damage to the nervous system (brain, spinal cord, peripheral nerves). It is different from pain messages that are carried along healthy nerves from damaged tissue (for example, a fall, cut, or arthritic knee).
How is the condition treated?
Neuropathic pain is treated with different types of medicines. Only a minority of people with neuropathic pain experience sufficient pain relief with the medications available.
Several products based on the cannabis plant have been suggested as treatments for neuropathic pain. These products include inhaled herbal cannabis and various medications (sprays, tablets, creams, transdermal patch (a medicated patch stuck to the skin)) containing active cannabis ingredients obtained from the plant, or made synthetically.
Cannabis-based products may contain: mainly tetrahydrocannabinol (THC), one main component of the cannabis flower; mainly cannabidiol (CBD), another main component of the cannabis flower; or a balanced ratio of THC and CBD.
Some people with neuropathic pain claim that cannabis-based products are effective for them. These claims are often highlighted in the media.
What did we want to find out?
We wanted to find out:
which components of the cannabis flower (if any) help reduce neuropathic pain;
if cannabis-based medicines cause any unwanted or harmful effects.
What did we do?
We searched for studies that compared different types of cannabis-based medicines (products including mainly THC or CBD and products including a balanced ratio of THC and CBD) against an inactive, fake medication, known as a 'placebo'.
We compared and summarised their results, and rated our confidence in the evidence, based on factors such as study methods and sizes. We analysed three comparisons:
THC-dominant medicines versus placebo;
THC/CBD-balanced medicines versus placebo;
CBD-dominant medicines versus placebo.
What did we find?
We found 21 studies that involved 2187 people with different types of neuropathic pain. The studies were conducted in Asia, Europe, and North America. The smallest study had 18 participants; the largest, 339 participants. Participants' average age ranged from 34 to 70 years. The proportion of women ranged from 0% to 90%. Studies lasted between two and 26 weeks. Pharmaceutical companies funded 14 (or two-thirds) of the studies.
Main results
THC-dominant medicines versus placebo
It is unclear if medicines with mainly THC make any difference to the number of people who:
experience pain relief of at least 30% or at least 50%;
rate their condition to be much or very much improved;
stop the medication due to unwanted effects;
experience serious unwanted or harmful effects;
experience unwanted psychological effects (e.g. confusion).
THC-dominant medicines may slightly increase the number of unwanted effects of the nervous system (e.g. dizziness) compared to placebo.
THC/CBD-balanced medicines versus placebo
It is unclear if medicines with a balanced THC/CBD ratio make any difference to the number of people who experience:
pain relief of at least 50%;
serious unwanted or harmful effects;
unwanted effects of the nervous system (e.g. dizziness); and
unwanted psychological effects (e.g. confusion).
They may increase the number of people who rate their condition to be much or very much improved, experience pain relief of at least 30%, and stop the medication due to unwanted effects.
CBD-dominant medicines versus placebo
It is unclear if medicines with mainly CBD make any difference to the number of people who experience pain relief of at least 50%.
We do not know whether CBD-dominant medicines increase or decrease the number of people who:
rate their condition to be much or very much improved;
stop the medication due to unwanted effects;
experience serious unwanted or harmful effects;
experience pain relief of at least 30%;
experience unwanted psychological or nervous system-related effects.
This is because the evidence is limited, and the results vary between studies.
What are the limitations of the evidence?
Our confidence in the evidence is low to very low, and the results of further research could differ from the results of this review. Four main factors reduced our confidence in the evidence. Some studies did not clearly report how they were conducted. The results for many outcomes differed between studies. The results were also often not precise enough to draw firm conclusions. People with serious internal diseases (e.g. of the heart or liver) were excluded from the studies.
How current is the evidence?
The evidence is current to 29 January 2025.