More than half of people who use medical marijuana products to ease pain also experience clusters of multiple withdrawal symptoms when they're between uses, a new study finds.

And about 10% of the patients taking part in the study experienced worsening changes to their sleep, mood, mental state, energy and appetite over the next two years as they continued to use cannabis.

Many of them may not recognize that these symptoms come not from their underlying condition, but from their brain and body's reaction to the absence of substances in the cannabis products they're smoking, vaping, eating or applying to their skin, says the University of Michigan Addiction Center psychologist who led the study.

When someone experiences more than a few such symptoms, it's called cannabis withdrawal syndrome—and it can mean a higher risk of developing even more serious issues such as a cannabis use disorder.