A new study explains how regular marijuana use can fuel tumor growth in people with human papillomavirus (HPV)-related head and neck squamous cell carcinoma.

Previous studies have shown daily marijuana use is associated with an increased prevalence of HPV-related throat cancer. The reason for the link was unknown until now. In the new study, researchers from the University of California San Diego identified the molecular mechanism activated by THC, the psychoactive ingredient in marijuana. The findings appear in Clinical Cancer Research.

“HPV-related head and neck cancer is one of the fastest growing cancers in the United States. While at the same time, exposure to marijuana is accelerating. This is a huge public health problem,” Joseph A. Califano III, MD, senior author and professor and Vice Chief of the Division of Otolaryngology in the Department of Surgery at UC San Diego School of Medicine, said in a news release.

“We now have convincing scientific evidence that daily marijuana use can drive tumor growth in HPV-related head and neck cancer,” Califano said. “Marijuana and other cannabis products are often considered benign, but it is important to note that all drugs that have benefits can also have drawbacks. This is a cautionary tale.”