The study is one of the first into its pain-relieving properties despite many products being legalized and sold across the U.S.

Voters in Oregon, Washington and 20 other states have legalized medical and recreational marijuana, however the researchers, from Oregon Health & Science University (OHSU), found many products available in dispensaries have not been studied.

In the federally funded review, researchers trawled through 3,000 studies in the scientific literature up to January this year and found a total of 25 with scientifically valid evidence—18 randomized controlled studies and seven observational studies of at least four weeks.

They also found there was evidence to support a short-term benefit in treating neuropathic pain such as diabetic neuropathy which causes a burning or tingling sensation when the nerves become damaged.

The drugs found to be effective were tetrahydrocannabinol, or THC, and dronabinol (brand name Marinol) with nabilone (Cesamet).

Both products also led to notable side effects including sedation and dizziness, according to the review.

Another product, an under-the-tongue spray known as nabiximols, made of equal parts THC and cannabidiol, or CBD, also appeared to treat neuropathic pain.

This also led to side effects such as nausea, sedation, and dizziness.

Cannabis products are based on their ability to mimic the body's own endocannabinoid system.

This is comprised of receptors and enzymes in the nervous system that regulate bodily functions and can affect the sensation of pain.