Medicine for weight loss. Blue measure tape and capsule pills close-up.

Weight loss medications that mimic the hormone GLP-1 (glucagon-like peptide-1) in order to suppress appetite might also be triggering a variety of digestive problems, according to a new analysis of data from 5,411 patients.

The study found an increased risk of issues including pancreatitis, gastroparesis, and bowel obstruction in patients using GLP-1 medications, compared with a medication that doesn’t activate the same chemical pathways as GLP-1.

Although the risk is increased for these drugs, it’s still relatively small. For example, 0.8 percent of people taking Saxenda (a GLP-1 treatment) reported bowel obstructions, compared with 0.17 percent of people taking Contrave (a non-GLP-1).

However, with growing numbers of people taking these medications, that’s still a leap – and a four-fold increase.

“When you have millions of people using these drugs, you know, a 1 percent risk still translates to many people who may experience these events,” epidemiologist Mahyar Etminan, from the University of British Columbia, told CNN.

Injected weight loss treatments such as Wegovy, Ozempic, Saxenda, and Victoza all amplify the effects of GLP-1: they slow the speed at which food passes through the stomach, keeping people feeling fuller for longer.

GLP-1 can also manage blood glucose levels, and is often prescribed to help with diabetes. In this particular study, Etminan and a team from Canadian institutions looked at patients who were obese but who didn’t have diabetes, to focus on the weight loss aspect of the drug.

These are not mild or insignificant digestive problems, so the benefit of the drugs may not outweigh the risk for everyone, the researchers suggest, as there are now many people taking these treatments to trigger weight loss.

It’s not the first time these issues have come up. Drug companies have acknowledged the problems with digestive complications, but say they are known side effects that should be considered when taking the treatments, and only affect a small fraction of people.

Earlier this year the Food and Drug Administration (FDA) in the US ruled that Ozempic should come with a warning attached, indicating that a variety of “gastrointestinal disorders” had been reported by users of the medication.

The study didn’t cover all GLP-1-related treatments, and didn’t dive too deeply into why these drugs are increasing the associated health risks – nor did it prove cause and effect – but it’s clear that this is an area that needs further investigation.

“Given the wide use of these drugs, these adverse events, although rare, must be considered by patients who are contemplating using the drugs for weight loss because the risk-benefit calculus for this group might differ from that of those who use them for diabetes,” write the researchers in their published paper.

The research has been published in JAMA.