How Long Does Metformin Stay in Your System? Plus, 5 Other Things to Know About Metformin

Metformin is one of the most commonly prescribed medications for Type 2 diabetes. But even if you’ve been taking metformin for a while, it’s only natural to have questions about it.

From how long it stays in your system to whether it affects your body weight or energy levels, understanding how metformin works can help you get the most out of treatment. Below, we answer six common questions about metformin.

1. How long does metformin stay in your system?

Metformin typically stays in your system for about 4 days after your last dose. This is based on its half-life, which measures how long it takes for half of the medication to leave your bloodstream. Metformin’s half-life is about 17 hours. And it takes about 4 to 5 half-lives to clear most of a medication from your system.

However, your kidney health plays a significant role in how quickly metformin is cleared from your system. This is because your kidneys are responsible for removing most of it. So if you have kidney problems, it may take longer to clear metformin. For this reason, you may be prescribed a lower dose to decrease the risk of serious side effects, such as lactic acidosis.

What’s more, some medications interfere with how quickly metformin is processed in your body. This can cause metformin to build up in your system. Some examples of medications that interact with metformin include:

• Ranolazine

• Vandetanib (Caprelsa)

• Dolutegravir (Tivicay)

• Cimetidine (Tagamet HB)

Tell your prescriber if you take any of these medications. They may need to adjust your metformin dose.

2. Does metformin cause weight gain?

Not typically. On the contrary, metformin may help some people lose weight. Some research suggests it may help your body burn more calories. It might also lower your appetite, causing you to eat less food. Additionally, some people might have a low appetite due to side effects such as nausea, vomiting, and heartburn.

Studies have shown that people taking metformin have lost an average of 4 lbs to 8 lbs. But how much weight you can lose while taking it depends on many factors. These can include your diet, activity level, and how you respond to the medication.

3. Does metformin make you sleepy?

Metformin isn’t commonly associated with sleepiness or drowsiness. However, some people taking it during clinical trials reported experiencing a lack of energy. This could be related to underlying health conditions, such as diabetes or sleep apnea, or the medication itself.

Research on metformin’s effects on sleep have shown mixed results. Some studies suggest that metformin may improve sleep quality. Others have noted potential disruptions to sleep patterns, which could make you feel sleepy the next day. There have also been occasional reports of insomnia from people taking metformin.

In some cases, metformin may indirectly contribute to feeling tired by causing other health conditions. For example, long-term use of metformin can lead to low vitamin B12 levels, which is known to cause fatigue. Metformin can also lead to lactic acidosis, though this is rare. Sleepiness and fatigue are potential symptoms.

EXPERT PICKS: WHAT TO READ NEXT

• Metformin safety: If you’re taking multiple medications, here are some metformin interactions you should know.

• Diabetes diet plan: When you’re living with diabetes, your diet is important. Review this meal guide for suggestions on what to eat.

• Metformin side effects: Some side effects are common when taking metformin. Learn more about what you can expect while taking this medication.

While it’s normal to feel tired once in a while, let your prescriber know if it becomes an ongoing issue for you. They’ll want to evaluate you to make sure there isn’t something more serious going on.

4. Is metformin insulin?

No, metformin isn’t a type of insulin. It’s an oral medication that belongs to a class called biguanides.

Metformin works by lowering the amount of glucose (sugar) your body makes or absorbs. It also helps your body use its own insulin better. Because of how it works, metformin can have synergistic effects with insulin. So you may be prescribed both medications together.

5. Can you take metformin without food?

Yes, you can take metformin with food. In fact, it’s recommended to take metformin with a meal to help reduce side effects such as nausea. However, you may want to avoid foods that can worsen nausea, such as high-fat or spicy foods.

6. Can you cut metformin in half?

It depends. Metformin comes in immediate-release (IR) and extended-release (ER) forms.

Some IR forms of metformin may be split in half. For example, if your tablets have a score line, you can probably cut it in half. But if you’re taking an ER version of metformin, don’t cut it in half. This could affect the way the medication works in your body and put you at risk for side effects.

Some IR tablets have a film coating, so cutting them might cause a bad taste in your mouth. It’s best to always check with your pharmacist or prescriber about whether you can cut your metformin tablets. If you’re having trouble swallowing the tablets, ask your prescriber about the oral liquid.

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Written by:

Kristianne Hannemann, PharmD

Kristianne Hannemann, PharmD, is a licensed pharmacist in California. She has been a retail pharmacy manager and staff pharmacist for over 7 years and has contributed drug information content to different health companies.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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