Can you take metformin without having diabetes?

Metformin is sometimes used in people without diabetes, particularly in those who are overweight or obese. In an outpatient study of more than 150 non-diabetic people with overweight, metformin users lost an average of 5.8 kg over six months, while the control group gained an average of 0.8 kg. People with severe insulin resistance benefited the most. That sounds impressive, but it was not a controlled randomised trial, so there may be other explanations for the difference.

Metformin is also being investigated in people with certain cancers. In uterine cancer, cell and patient data suggest that it inhibits a specific tumour-growth protein, but clinical evidence of benefit is lacking. In lung cancer, observational studies suggest better outcomes in diabetic patients using metformin in combination with chemotherapy or radiation. Whether this also applies to non-diabetics was still unclear in the available studies. Do not overestimate the status of this research: these are preliminary signals, not proven clinical benefits for non-diabetics.

There is also a safety signal you should be aware of. Animal studies and cell studies show that metformin at therapeutic doses directly affects the electrical activity of the healthy heart. It inhibits potassium channels that are needed for a normal heartbeat, which may increase the risk of a dangerous heart rhythm. This has not yet been established in healthy people, but it is a serious signal that deserves attention, especially in people without diabetes who use metformin without a clear medical indication.

In short: there is limited evidence for weight loss in people who are overweight, but the evidence base is thin and does not come from randomised trials. The potential cardiac risks are still uncertain but cannot be ignored. Taking metformin without diabetes is something you should only do in consultation with your doctor, not on your own initiative.