Metformin - Is it dangerous to take metformin when my blood sugar is not high?

It is not dangerous to take metformin when your blood sugar is in the normal range or when it is high.

I'm a patient and I take metformin for my diabetes. My experience is that, once you've been on the correct dosage of metformin for a while you will seldom have high blood sugar, so long as you keep taking the metformin regularly.

Some people are prescribed metformin for other reasons, such as treating PCOS, and they've never had high blood sugar, only ever normal blood sugar.

IF I have low blood sugar (less than 4 in Canadian units, less than 72 in US units), I skip my metformin dose until my blood sugar is back up. And when I've been told to fast for surgery, I've been told to not take my metformin (i.e. if you cannot eat then do not take the metformin) -- but I do not know if that is general advice for everyone. Ask your doctor or pharmacist when that eventually comes up.

"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."

Source: Harvard Health Publishing
Harvard Medical School