US scientists say there’s a link between heavy cannabis use and an increased risk of head and neck cancers. They looked at data for more than 4 million people, 116,076 of whom had a diagnosed cannabis-related disorder, defined as excessive use of the drug leading to social problems or struggles to hold down a job. They found the heavy cannabis users had an increased risk of all head and neck cancers, as well as oral, nasal, salivary gland, and larynx cancer, compared with a group of similar people from the non-cannabis group. However, this type of study cannot prove heavy cannabis use caused the increase in cancer risk, just that a link exists, and the authors say heavier tobacco and alcohol use among the cannabis users may have influenced the results. As cannabis use becomes more acceptable in many parts of the world, the authors stress the need to investigate links to ill health thoroughly.
