A popular diabetes drug can provide protection against skin cancers, a new study says.

Metformin significantly reduces people’s risk of developing basal cell cancers or squamous cell cancers, the two most common skin cancers, researchers found in a recent study published in the Journal of Drugs in Dermatology.

People taking metformin had a significantly lower risk of basal cell cancer and a significantly lower risk of squamous cell cancer, results show.

“This study strengthens the evidence supporting metformin's potential as a protective agent against non-melanoma skin cancer,” concluded the research team led by senior researcher Dr. Tiffany Libby, an assistant professor of dermatology with Brown University.

Metformin is now the most widely prescribed pill for Type 2 diabetes, researchers said in background notes.

Previous studies have suggested that metformin might lower a person’s risk of skin cancer.

About 5.4 million basal and squamous cell skin cancers are diagnosed each year in the U.S., according to the American Cancer Society. Of those, 8 out of 10 are basal cell cancers.

Deaths from these skin cancers are not common. Only about 2,000 to 8,000 people a year die from skin cancers that aren’t melanoma, which is much more dangerous, the ACS says.

For this study, researchers compared a healthy control group against more than 8,000 people diagnosed with basal cell cancer and more than 4,100 patients with squamous cell cancer.

Each person with skin cancer was matched with four other healthy people who shared their age, race, ethnicity and sex, researchers said. The patient data came from a diverse health database maintained by the National Institutes of Health.

Results showed that metformin users did indeed have a lower risk of skin cancers, especially after researchers adjusted for other medications that can increase risk of skin cancer.

However, the drug did not protect Black patients against squamous cell cancers, researchers found.

“This discrepancy could stem from the fact that SCC in these patients often develops in sunprotected areas and is strongly linked to chronic scarring and inflammation, factors that may not be influenced by metformin use,” the research team wrote.

Metformin might protect against skin cancer by regulating mechanisms that block cancer cells’ access to energy and nutrients, or by blocking the ability of cancer cells to grow and proliferate, researchers said.

Metformin also promotes the death of unhealthy cells, enhances the body’s immune response against cancer cells, reduces inflammation and inhibits the growth of new blood vessels to skin tumors.

“In conclusion, our results suggest that further research may be warranted to consider metformin as a chemopreventive agent,” the researchers concluded.