I heard that metformin is is a bad drug and not good to take. Is that true?

Metformin is the safest drug to use for Type 2 diabetes. That is why it is the drug usually prescribed first.

I don't have an opinion on the safety of metformin for other uses.

Is metformin a wonder drug?

Ever wonder why certain medications are called "wonder drugs"?

Sometimes it's because of the tremendous health benefits the drug provides for a particular condition, like insulin for type 1 diabetes or antibiotics for pneumonia. Or, it might be because the drug is good for many different conditions: aspirin has often been called a wonder drug because it can relieve pain, treat or prevent cardiovascular disease, and even prevent cancer.

Could metformin be joining this list? It's approved in the US to treat type 2 diabetes when used with diet and exercise by people ages 10 and older. But in recent years, interest has grown regarding its potential to prevent or treat a variety of other conditions, including aging. Yes, aging. If that's true, "wonder drug" might be an understatement.

Metformin's benefits may extend far beyond diabetes
For decades we've known that metformin does more than just help lower blood sugar in people with diabetes. It also offers them cardiovascular benefits, including lower rates of death due to cardiovascular disease. And it sometimes helps people with diabetes lose excess weight.

Metformin may also have health benefits for people who don't have diabetes. Doctors have long prescribed it off-label — that is, to treat conditions outside its approved use, including:

Prediabetes. People with prediabetes have elevated blood sugar that isn't yet high enough to qualify as diabetes. Metformin may delay the onset of diabetes or even prevent it among people with prediabetes.
Gestational diabetes. Pregnant women may develop elevated blood sugar that returns to normal after delivery. Metformin can help control blood sugar during pregnancy in such women.
Polycystic ovary syndrome (PCOS). This disorder tends to affect young women whose ovaries develop multiple cysts. Menstrual irregularities and fertility problems are common. Although the results of clinical studies are mixed, metformin has been prescribed for years for women with PCOS to help with menstrual regulation, fertility, and elevated blood sugar.
Weight gain from antipsychotic medicines. Antipsychotics are powerful medications prescribed for psychiatric diseases such as schizophrenia. One common side effect is significant weight gain. Metformin may lessen weight gain among some people taking these drugs.
In addition, researchers are investigating the potential of metformin to

Lower the risk of cancer in persons with type 2 diabetes. These include cancers of the breast, colon, and prostate.
Lower risks for dementia and stroke. Some studies have noted less cognitive decline and a lower rate of dementia, as well as a lower rate of stroke, among people with diabetes taking metformin compared with those who were not taking it.
Slow aging, prevent age-related disease, and increase lifespan. Preliminary studies suggest that metformin may actually slow aging and increase life expectancy by improving the body's responsiveness to insulin, antioxidant effects, and improving blood vessel health.
Because the vast majority of research regarding metformin included only people with diabetes or prediabetes, it's unclear whether these potential benefits are limited to people with those conditions, or whether people without diabetes may derive benefit as well.

Source: Harvard Health Publishing
Harvard Medical School