Obesity is the second biggest preventable cause of cancer in the UK after smoking. So can medications that help people lose 20% of their body weight also reduce cancer risk? The answer is more nuanced than you might expect.1
The logic seems straightforward — but it's unproven
We know that being overweight increases the risk of at least 13 types of cancer, including breast, bowel, womb, kidney, and pancreatic cancer. We also know that the risk depends on both the degree of excess weight and how long someone is overweight for. Logically, losing weight should reduce that risk. However, as Cancer Research UK noted in February 2026, "it's actually not been explicitly proven that these drugs reduce cancer risk" — it's assumed based on the weight loss, but not yet demonstrated in dedicated studies.1
The thyroid question
In the US, semaglutide (Wegovy/Ozempic) carries a boxed warning about thyroid C-cell tumours, based on findings in rodent studies where the medication caused thyroid tumours in rats. However, human studies — including a recent review of 48 trials — have not found evidence of increased thyroid cancer risk in humans. The warning is not applied in the UK or EU. The rodent findings may be species-specific.2
Potential protective effects
A large 2025 study published in Nature Medicine looking at health data from over 2.4 million people found that GLP-1 medications were associated with reduced risk of 42 different health conditions, including some cancers. However, this was observational data — it shows association, not causation — and much more research is needed before any cancer-prevention claims can be made.3
The bottom line
It's plausible that GLP-1-related weight loss may reduce cancer risk over the long term, but this hasn't been proven yet. Dedicated long-term studies are needed. In the meantime, the established health benefits of weight loss (cardiovascular, metabolic, musculoskeletal) remain the primary reasons for considering treatment.