Popular weight-loss drugs may lower cancer risk, finds large study

Weight-loss drugs known as GLP-1 receptor agonists are discussed for their effect on blood sugar and body weight. A large new study, published in JAMA Network Open in 2024, adds another layer to the conversation. Researchers looked at whether these drugs are linked to a lower risk of certain cancers that are strongly tied to obesity.

The results are encouraging in parts, cautious in others, and far from a green light for everyone.

What the study actually set out to test

Scientists focused on 13 cancers that are known to be linked with obesity. These include cancers of the colon, liver, pancreas, kidney, uterus, and a few others. The key question was simple but important: do people with type 2 diabetes who take GLP-1 drugs develop these cancers less often than those treated with insulin or metformin?To answer this, researchers analysed electronic health records from across the US.

The dataset covered more than 1.6 million adults with type 2 diabetes, followed for up to 15 years. None had a prior diagnosis of these cancers at the start.

The strongest signal: GLP-1 drugs vs insulin

When GLP-1 drugs were compared with insulin, the difference was clear for many cancers. People on GLP-1 medicines had a significantly lower risk of 10 out of the 13 obesity-associated cancers.The largest risk reductions were seen in gallbladder cancer, meningioma, pancreatic cancer, and liver cancer.

For example, the risk of gallbladder cancer was about 65 percent lower, and pancreatic cancer risk was reduced by more than half compared with insulin users.These are not small changes. They suggest that, for people with type 2 diabetes, the choice of diabetes treatment may influence long-term cancer risk.

Where the benefits did not show up

The findings were not uniformly positive. GLP-1 drugs did not lower the risk of postmenopausal breast cancer or thyroid cancer when compared with insulin.

Stomach cancer showed a trend toward lower risk, but the result was not statistically strong enough to be certain.This matters because it shows the effect is selective, not universal. These drugs are not acting as broad cancer-prevention medicines.

A critical comparison: GLP-1 drugs vs metformin

Metformin is often the first drug prescribed for type 2 diabetes, and it already has a reputation for possible cancer-related benefits. When researchers compared GLP-1 drugs with metformin, the picture changed.There was no clear reduction in cancer risk with GLP-1 drugs compared with metformin for any of the cancers studied. In fact, kidney cancer risk was higher in the GLP-1 group compared with metformin users. This does not prove harm, but it does raise an important red flag for further study.In simple terms, GLP-1 drugs looked better than insulin, but not better than metformin.

What may explain these results

The study did not prove why these differences exist, but a few clues stand out.

GLP-1 drugs help reduce body weight, improve insulin sensitivity, and lower chronic inflammation. All three factors are linked with cancer risk in obesity.Insulin therapy, on the other hand, can lead to weight gain and higher insulin levels in the body, which may promote tumour growth in some tissues. Metformin works through different pathways, which may explain why GLP-1 drugs did not outperform it.These are still theories, not confirmed answers.

What this study does and does not mean

This research offers strong clinical signals, but it does not prove cause and effect. It was a retrospective study, meaning researchers looked back at existing records rather than assigning treatments randomly.The results suggest that GLP-1 drugs may offer added protection against certain obesity-linked cancers for people with type 2 diabetes, especially when compared with insulin. They do not suggest these drugs should be used solely to prevent cancer, or that they are safer or better for everyone.More controlled clinical trials are needed before any firm conclusions are made.Disclaimer: This article is for informational purposes only and is based on published research data. It does not provide medical advice. Treatment decisions should always be made in consultation with a qualified healthcare professional, considering individual health needs and risks.