There is no clear evidence that cannabis-based medicines provide pain relief for chronic neuropathic pain, an updated Cochrane review finds.
Chronic neuropathic pain is caused by nerve damage. Existing medications help only a minority of patients, driving interest in alternatives, such as cannabis-based medicines. These can include herbal cannabis or isolated ingredients of the cannabis plant such as tetrahydrocannabinol (THC) by inhalation, mouth sprays, tablets, creams, and patches placed on the skin.
Researchers reviewed 21 clinical trials involving more than 2,100 adults, comparing cannabis-based medicines with placebo over periods of two to 26 weeks.
Cannabis-based medicines were grouped into three types: products which contain mostly THC, the psychoactive component of cannabis; products which contain mostly cannabidiol (CBD), a non-intoxicating compound; and balanced THC/CBD products, which contain similar amounts of both.
The review found no high-quality evidence that cannabis-based medicines reduce neuropathic pain more than placebo across the three types of medicines. While some small improvements were reported by patients using products with both THC and CBD, these changes were not large enough to be considered clinically meaningful.
Reporting of adverse events was not consistent across the included trials, so certainty around side-effects was low to very low across all types of cannabis-based medicines. Products containing THC were associated with increases in symptoms such as dizziness and drowsiness, with a potential increase in the number of people withdrawing from trials due to side effects.
"We need larger, well-designed studies with a treatment duration of at least 12 weeks that include people with comorbid physical illnesses and mental health conditions to fully understand the benefits and harms of cannabis-based medicines," said Winfried Häuser, clinician and lead author, from Technische Universität München and Medical Center Pain Medicine and Mental Health Saarbrücken. "At present, the quality of most of the trials is too poor to draw firm conclusions."
The authors conclude that the evidence remains weak and uncertain, underscoring the need for higher-quality research before cannabis-based medicines can be recommended for chronic neuropathic pain.
