Metformin is one of the original diabetes drugs. It’s been around for decades, and is still the go-to medication for people with prediabetes and type 2 diabetes. And no wonder: It lowers blood sugar (aka glucose) in everyone with these conditions, says Nicole Paolini Albanese, PharmD, a clinical associate professor at the School of Pharmacy and Pharmaceutical Sciences at the State University of New York at Buffalo.

Normally, your body converts the food you eat into glucose, which it then uses for energy or stores for later. But when you have prediabetes or type 2 diabetes, that process is impaired. Cells aren’t able to access the glucose as efficiently, which means you end up with too much sugar in your blood. If left untreated, diabetes can cause cardiovascular problems such as heart attacks and strokes. It can also cause kidney failure, blindness, and nerve damage in your legs and feet.

Metformin (Fortamet, Glucophage) works to regulate blood sugar in two ways. “The first and most pronounced thing that it does is that it shuts (down) your liver’s production of sugar,” says Albanese. When you’ve gone a long time without eating, your liver taps into your stored energy sources and pumps out glucose to power your cells. But if you have type 2 diabetes, you don’t need this extra sugar — you already have too much circulating in your blood.

Metformin also helps with insulin resistance, says Albanese, which is what happens when insulin, a hormone produced by the pancreas, can no longer move glucose from your blood to your cells. As your cells absorb less sugar, it builds up in the blood. Metformin reverses that process.

Your doctor will probably start you off on a low dose and work you up to the maximum dose over a period of 4 weeks, and that’s where you will stay (if you can tolerate it) for the rest of your life. Here’s what you can expect from the first day.

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Day one

You’ll take your 500-mg pill with your biggest meal of the day, either breakfast or dinner, whichever is more substantial, says Albanese. And by substantial, she doesn’t mean a piece of fruit or a handful of chips, but a sit-down meal like a bowl of chili or even a salad. “It doesn’t have to be heavy,” Albanese says. “It just needs to be a good amount of food.”

Metformin starts working on your liver and insulin right way, but you won’t notice the effects yet: “The deficiencies [in your ability to regulate blood sugar] are so great that one dose of it isn’t going to affect any real change,” says Albanese. You may have a metallic taste in your mouth the next day, thanks to metformin in your saliva, but that’s about it, she adds. (The metallic taste should go away as your body adjusts to the medication.)

You will continue to take one pill a day for a week.

Week two

You’re going to start taking two tablets, one at breakfast and one at dinner, as long as those meals are more or less 12 hours apart. This is when you might start noticing some side effects, which are all gastrointestinal (GI)—queasiness, diarrhea and gas, mostly, though a few people actually throw up.

Why the gastro distress? “It’s related to how metformin physically moves through the body. It breaks down in the stomach and is being released there, whereas a lot of other drugs keep moving and they don’t open up until they reach the intestines, so they don’t have those GI issues,” says Albanese.

Weeks three and four

You’ll be adding another 500-mg tablet each week. The third week, you’ll be taking three tablets, two at the largest meal and then one in the morning (or evening, depending on which meal is actually a sit-down one). The fourth week, you’ll be taking two tablets twice a day, or four total.

During these weeks, your GI issues will reach their peak. This could mean more gas, nausea and diarrhea. One thing that helps, says Albanese: “I will have them eat their complete meal so that there is this base of food there, and then take the pill. Normally people can just take it with the first bite of the meal, but it does take your stomach time to break down your food. So that timing could help.”

But aside from that, you’ll just have to try to power through for a few weeks, she says—no over-the-counter drug, even Pepto Bismol, is going to do you any good (the pathways these drugs take are different). The good news: The side effects do subside for most people.

Plus, metformin should start working its magic by the end of the second week. “If somebody is checking their blood sugar at home with a meter, they might notice on average their levels are down maybe 5, maybe 10 points,” says Albanese.

Month two and beyond

By now, your side effects should have leveled off because your body has gotten used to the drug. If you still can’t handle the GI issues a couple of weeks after taking the full dose, talk to your pharmacist or provider.

“Then we reduce the dose, so instead of being on 2,000 mg, we can push it back to 1,000 mg a day, and most people are able to tolerate that,” says Albanese. (If you still can’t, your provider will probably take you off metformin.)

With metformin, your A1C (Glycated hemoglobin) can be reduced between 1 and 1.8 points, says Albanese. And you may even lose a little weight. How much is a little? Between 4 and 8 pounds or so.

Here are the other long-term benefits you can expect:

  • You’ll have more energy as your body uses insulin more efficiently.
  • Common diabetes-related symptoms, such as blurry vision, being thirsty all of the time, or having to pee a lot, improve or disappear.
  • After a few years of treatment, your risk of having a stroke or heart attack goes down significantly, according to a 2020 study published in Diabetes Research and Clinical Practice.

One slight drawback with metformin is it can decrease your vitamin B12 levels, says Albanese. “So we need to check those on people every two or three years, and if they need some supplementation, then we can give it to them.”

You’ll still have to pair metformin with changes to your diet and exercise routines to really keep your condition in check. Eat more fruits, vegetables and whole-grain carbs, less processed foods and sugary snacks, and get your heart rate up on most days by walking, dancing or riding a bike. Your body will thank you!