Metformin lowers blood sugar levels. It is therefore the first choice in the treatment of type 2 diabetes, also known as diabetes. In addition to this effect, experts have for some time speculated about a possible beneficial side effect of the drug: protection against cancer.
Some studies show that people who regularly take metformin are less likely to develop cancer than others. So can diabetes drugs also benefit healthy people without diabetes?
Metformin and cancer: conflicting results
We set out to find reliable scientific papers that could answer this question. There seems to be a lot of research on this [1,2], our extensive research showed. However, this paints a contradictory picture:
Certain types of cancer, such as liver and colon cancer, actually occur less frequently in metformin users. However, this effect does not appear to exist in other types of cancer, such as pancreatic cancer or ovarian cancer.
Is the anti-cancer effect just an anti-diabetic effect?
However, we are not confident in these results. The researchers behind these studies compared the cancer risk of diabetics who took metformin with diabetics who did not take diabetes medications or did not take other diabetes medications. So more than metformin, successful treatment of diabetes reduced the risk of cancer.
Comparing apples to oranges
In addition, the more than 160 studies conducted so far on metformin and cancer are very different. It is therefore very difficult to summarize their results in a meaningful way – it is the proverbial comparison of apples and oranges.
Studies in healthy people are lacking
But how can one meaningfully investigate whether metformin protects against cancer? This requires studies involving healthy people without diabetes. Half of the participants would take metformin long-term, and the other half would not. Because many types of cancer develop slowly, these studies need to run for a very long time. A comparison would then be made: were there fewer cancer cases with metformin than without?
No such studies seem to exist. Most of the available studies were primarily interested in the efficacy of metformin against diabetes and only examined cancer as a potential side effect of the drug.
Conclusion of studies
There is no general answer to whether metformin actually protects against cancer. For example, there are warning signs that people who use metformin are less likely to develop cancer of the digestive tract. [1]. But it is not guaranteed. We explain why in more detail in the “Detailed Studies” section. It's not entirely clear whether people without diabetes benefit from the drug when it comes to cancer. We could not find any studies on this.
Safe information about diabetes and its treatment
People with type 2 diabetes can find science-based information, for example, on the health portal Gesundheitsinformation.de or on Gesundheit.gv.at.
Metformin for Cancer: How Is It Supposed to Work?
Experts suspect that metformin may reduce the risk of cancer by inhibiting the growth of cells [4]. It activates a signaling molecule in our cells that, among other things, inhibits cell growth. This molecule is intended to prevent cells from proliferating uncontrollably – as they do in malignant tumors. However, this growth-inhibitory effect of metformin has so far only been shown in animal experiments with worms. Whether it has the same effect in humans is uncertain.
A well-researched drug
Metformin has been used as a diabetes medication for over 70 years and has been well researched. The most unpleasant side effects include digestive problems. However, these usually occur early in treatment and improve later.
Because metformin can cause low levels of vitamin B12 in the blood, vitamins may need to be taken as a dietary supplement.
Very rarely, metformin can cause a life-threatening acidification of the blood, known as acidosis. Alcohol in particular increases the risk of such acidosis. Therefore, metformin users should avoid alcohol or drink only small amounts [3].
