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9 FAQs for Anyone Taking Metformin (Glucophage)

Answers to the most frequently asked questions about metformin

Metformin (Glucophage) is a medication that can be used to treat type 2 diabetes or to help prevent it in patients at a high risk of developing it. Metformin lowers blood sugar and boosts the body's ability to respond to insulin. It is prescribed as a tablet or a liquid form. In many cases, a healthcare provider prescribes metformin only after lifestyle changes, such as an improved diet and exercise, have been tried and shown not to be effective enough. Other than its approved uses, metformin (Glucophage) is sometimes used to treat polycystic ovary syndrome or PCOS. PCOS is a condition that affects how the ovaries work. Aside from lowering blood sugar levels and improving the way your body responds to insulin, metformin can also stimulate ovulation, which aids in the treatment of PCOS. On this page, we will dive into nine of the most common questions asked by patients that have been prescribed metformin.

The content on this page is provided for informational purposes only. If you have any questions or concerns about your treatment, you should talk to your doctor, pharmacist, or healthcare professional. This is particularly important if you are taking multiple medications or have any existing medical conditions.

What is metformin (Glucophage) and how does it work?

Metformin is one of the most prescribed drugs on the market for patients with type 2 diabetes. It has three primary mechanisms of action that make it effective in treating patients. It decreases blood sugar production in the liver, which helps prevent hyperglycemia. Second, it increases the sensitivity of the cells responsible for processing insulin, which is part of why it is often an earlier step than prescribing insulin itself (although they are often prescribed together as well). Additionally, it decreases glucose absorption in the intestines. All three of these mechanisms of action together make it effective in regulating blood sugar and properly making use of insulin.

When should I take metformin?

If possible, you should try and take metformin with a meal to reduce the side effects. As the maximum daily dose is 2000 mg, which can come in 4 separate doses, it may not be practical to eat with each of them. However, if you are taking a smaller daily dose or taking a slow-release tablet the best way to do it is to take it with your evening meal. That said, due to the variety of dosing possibilities the best thing to do is ask your doctor for advice about when to take metformin.

How long does it take for metformin to work?

Metformin acts relatively quickly. You could potentially see effects within the first 48 hours of use but for the medication to take full effect it typically takes four to five days. This can also vary depending on the dosage you are taking. Usually, doses will start out small, in order to mitigate the adverse side effects. This also means that the intended effects of the drug will take more time, especially regarding blood sugar. Patients often start with a dose of around 500 milligrams a day and do not report lower blood sugar until they have started taking 1500 milligrams a day.

What are the side effects of metformin?

Metformin can produce a range of side effects. Some of the more common side effects may not be something to be concerned about, but if they persist for weeks or become more severe you should speak with your doctor.

Common side effects:

  • Diarrhea
  • Headaches
  • Nausea
  • Nosebleeds
  • Sore throat or congestion
  • Constipation
  • Stomach upset

Severe side effects:

  • Intense muscle cramps or pain
  • Dark urine
  • Yellowed eyes or skin
  • Intense stomach pain
  • Unintended weight loss
  • Shortness of breath

If you experience any of these severe side effects, talk to your doctor immediately.

Allergic reaction – In some rare cases, patients can experience allergic reactions. Seek emergency medical care if you experience any of the following symptoms after taking metformin.

Skin rash


Tightness in the throat or chest

Difficulty talking or breathing

Swelling of the face, lips, tongue, or throat

This is not a complete list of the possible side effects of metformin. For more information, you should speak to your doctor or read the patient information label.

If you have poor kidney function, your healthcare provider may choose not to prescribe metformin due to the risk of lactic acidosis; however, this will be determined on a case-by-case basis. The risk of lactic acidosis from metformin also increases with excessive alcohol intake.

Metformin may also reduce vitamin B12 levels, causing vitamin B12 deficiency. This deficiency can result in anemia.

How long do metformin side effects last?

If you have been experiencing any side effects of metformin, especially the unpleasant ones, you would probably like to know when they will end. The good news is, that on average, most side effects resolve themselves within a couple of weeks, though they may reoccur if your dosage is increased.

For some patients, it takes longer than two weeks for side effects to go away. However, if they simply will not go away there are methods to better cope with the side effects. If you notice stomach upset from metformin, ask about switching to the extended-release (ER) version. Metformin ER is less likely to cause stomach upset.

If you have been vomiting or experiencing diarrhea, be sure to stay hydrated and take your medication with a meal whenever possible. Some patients may find this difficult if they have been experiencing a loss of appetite, another common side effect. Consider eating smaller meals more frequently throughout the day than you typically would. Another common but potentially frustrating side effect is a metallic taste in the mouth. If this taste will not go away, try chewing sugar-free gum or mints.

If side effects are persistent, worsen, or you are finding them difficult to cope with, you should speak to your doctor.

What drugs should I not take with metformin?

There are several drugs that could potentially interact with metformin. We have listed below some of the most common. However, this is not a complete list and you should inform your doctor about any medications (including over-the-counter drugs and supplements) you are taking before you start taking metformin. If you are taking a drug that may interact with metformin, your doctor may choose to switch your medication, increase or decrease your medication dose, or prescribe a higher or lower dose of metformin.

Below are some drugs that may have negative interactions with metformin.

  • Beta-blockers, like atenolol and propranolol
  • Fluoroquinolone antibiotics, like ciprofloxacin and levofloxacin
  • HIV antiretrovirals, like dolutegravir and ritonavir
  • Linezolid
  • Selegiline
  • Verapamil
  • Dofetilide

How do I take metformin?

Metformin is prescribed in either pill form or liquid form. Do not chew metformin pills, as chewing can reduce the effectiveness of the dose. The liquid form is less common, but it is worth noting that it should be measured carefully. This means using a proper tool such as a dropper, not a spoon. Take either form of the medication with a meal whenever possible. If you are only taking one dose per day it is recommended to take it each evening with your nightly meal. Another common concern is, “what if I miss a dose of metformin?” Simply take the next dose at the usual time. Do not, however, attempt to make up for a missed dose by taking two at once. If you have taken a double dose or any more than prescribed seek medical attention as it can cause severe health problems that onset quickly.

Why does metformin cause diarrhea?

If you are taking or have just been prescribed metformin you may know that a possible side effect is diarrhea. If so, you almost certainly would like to better understand why that happens. Unfortunately, the underlying mechanism behind metformin is unknown. There is, however, a popular hypothesis that it has to do with the malabsorption of bile salts that can be caused by metformin, which can then lead to diarrhea.

The best ways of mitigating the risk of diarrhea when taking metformin are to stay hydrated and to take your doses with food.

Can I drink alcohol with metformin?

Drinking alcohol with metformin is okay as long as it is in moderation. Drinking excessively, or more than two units per day, can result in lowered blood sugar or lactic acidosis. It is best to try and drink no more than 14 units each week. For reference, a pint of beer is usually 2 to 3 units. If you plan to drink while taking metformin, it’s a good idea to talk with your healthcare provider about how you can do so safely.

The content on this page is provided for informational purposes only. If you have any questions or concerns about your treatment, you should talk to your doctor, pharmacist, or healthcare professional. This is particularly important if you are taking multiple medications or have any existing medical conditions.