People who take metformin for diabetes management will often take the medication once or twice per day, or up to three times daily for higher doses.
In some cases, however, people may take slow-release metformin tablets (also known as extended-release, ER, or XR), which can be taken less often.
This is normally straightforward. However, it is important to know how long metformin stays in your system for a variety of reasons. This article will investigate how long the medication is active in your body after you’ve taken it or after you’ve stopped taking it.
Table of Contents
Why is it important to know how long metformin stays in your system?
Taking medication every day can be difficult. Indeed, life can sometimes get in the way of taking medications as prescribed and on time.
Metformin is generally best taken once or twice daily. (Be sure to check with your doctor about the schedule that is best for your situation.)
But without knowing how long it stays in your system, it can be difficult to know how and when to take your medicine if you’re trying (in consultation with your healthcare team) to raise or lower your dose or to wean yourself off metformin altogether.
It is additionally helpful to know how long metformin lasts in your system if you’ve forgotten to take your medication, if you are wondering when it is safe to take your next full dose, or if you’re not sure whether the metformin you’ve previously taken will interact with other medications or food or alcohol you plan to consume.
Does metformin take a while to build up in your system?
Yes, and if you’ve just started taking metformin, you most likely won’t notice improved blood sugar levels or weight loss immediately, no matter what dose you are taking.
The first effects on blood sugar levels may be noticed within 48 hours of starting the medication, but the most significant effects won’t be seen until after 4-5 days of consistently taking the medication.
Any expectations of weight loss, however, may take several weeks or months to come to fruition and will require changes in diet and exercise as well. It’s also important to note that the weight-loss generally associated with metformin is modest — in the range of 5 pounds.
Read more in: Signs Metformin Is Working (Or Isn’t Working)
A potentially dangerous buildup of metformin in the body can happen if your kidneys are not properly functioning to process the medication. This can result in a condition called lactic acidosis (a buildup of lactic acid in the bloodstream), which can be life-threatening.
Contact your doctor if you’re experiencing symptoms of lactic acidosis, including:
- Feeling disoriented
- Rapid breathing
- Rapid heart rate
- Abdominal pain
- Headache
- Lethargy and fatigue
- Muscle cramps and muscle pain
- Body weakness
- Reduced appetite
- Diarrhea
- Vomiting
- Nausea
- Yellowing of the skin or eyes
Some of these symptoms can be confused with normal metformin side effects, but take note if you start to experience any new symptoms after you’ve been on metformin for a while.
(All this being said, metformin is generally a very safe drug, and most people experience minimal side effects.)
Read more in: Is Metformin Safe?
How long do metformin side effects last?
Typically, side effects of metformin, such as vomiting, diarrhea, nausea, stomachache, and loss of appetite, go away after a few weeks on the medication.
For those who experience significant side effects, there are good alternatives to metformin, including several metformin combination drugs that may have fewer side effects.
Learn more in: Metformin Combination Drugs for Type 2 Diabetes.
Metformin half-life
The half-life of a medication is the time it takes for 50 percent of the drug’s active ingredient to be metabolized or eliminated from your body.
Metformin has an elimination half-life from red blood cells of approximately 17.6 hours. (It is important to note, however, that this figure may vary between different formulations of the medication, such as extended-release versus immediate-release.)
The average elimination half-life of metformin in plasma (the liquid portion of blood) is only 6.2 hours, but most of the active ingredients in metformin accumulate in the red blood cells (RBCs), so that is where we will focus.
This means that every 17.6 hours, the drug becomes 50 percent less strong. However, there are some caveats.
Does metformin stay in some people’s systems longer than others?
Yes. The half-life of metformin is not an exact science because everyone is different. Metformin tends to remain in the bodies of certain populations for a longer time.
People with renal (kidney) impairment
For people living with kidney disease or kidney failure, metformin will stay in the body much longer.
For people taking metformin who have mild kidney failure, the oral clearance (the rate at which the body processes and absorbs metformin from the gastrointestinal tract into the bloodstream) and renal clearance (the rate at which the kidneys eliminate metformin from the body) of metformin is decreased by 33 percent and 16 percent, respectively.
For those with moderate kidney failure, the oral clearance and renal clearance of metformin are decreased by 50 percent and 53 percent, respectively.
Age
Older people tend to have metformin stay in their system longer than younger people. This has a few causes, but the major one is decreased kidney function as people with diabetes age.
For that reason, it is recommended that metformin should not be started in people who are 80 years and older unless creatinine clearance (a measure of how well the kidneys filter creatinine out of the bloodstream) can show that kidney function is not reduced.
Metabolic rate
People who have a slower metabolic rate will have metformin in their system for longer. This is because the body is processing everything (including food, alcohol, and medications) more slowly.
Compared to people without diabetes, those with type 2 diabetes who take metformin will have the medication in their system for longer, even after stopping the drug.
See more in: Stopping Metformin: When and How You Can Stop Taking Metformin.
Body mass
The higher your body mass, the longer metformin will stay in your system. This applies to all medications.
If your body mass is higher, you’re also more likely to be taking a larger dose of metformin, which will affect the time it spends in your system as well.
Dose
If you’re on a low dose of metformin, the duration it stays in your system is lower than for someone who is on the maximum daily dose of metformin, which is roughly 2,550 milligrams (mg) per day.
If you’re taking the maximum dose, expect the medication to stay in your system much longer than it does for someone who may be taking only, say, 500 mg per day.
How long you’ve taken the drug
If you’ve been on metformin for 10 years and stop taking it, the drug may stay in your system for longer than it does for someone who took the medication for one week and then stopped.
While medications take a while to build up in the system, they also take a while to break down, even if you’re not actively taking the medication.
How long does it take metformin to get out of your system?
It takes approximately 5.5 times the elimination half-life for metformin to be completely cleared from your body which is:
5.5 x 17.6 hours = 96.8 hours
That being said, it is completely fine (and expected) for you to take your metformin dose more often than every 4 days, but this is how long it would take to completely clear from your body if your kidneys are functioning properly.
Different systems in the body may clear metformin faster than others, but within 4 days, you will have a negligible amount of metformin left in your body.
Frequently asked questions
Can I mix metformin with other medications?
Metformin can negatively interact with other prescribed medications, so always tell your doctor about all medications you currently take if you’ve recently been prescribed metformin. If you’re on metformin, make sure you tell your doctor before starting any new medications.
Metformin can interact with:
- insulin
- sulfonylureas chlorpropamide (brand name Diabinese)
- glimepiride (Amaryl)
- glipizide (Glucotrol)
- glyburide (DiaBeta, Glynase, Micronase)
- tolazamide (Tolinase)
- meglitinides (repaglinide [Prandin] and nateglinide [Starlix])
It may also interact with diuretics, steroids, and corticosteroids.
It can sometimes interact with substances in such a way that the risk of lactic acidosis (which, as noted earlier, can be fatal) is increased.
Your doctor may want you to completely be weaned off metformin before starting another drug.
I forgot to bring my metformin on vacation. How long will it last?
Metformin will be active in your body for 4 days, but you may notice higher blood sugar levels within 1 or 2 days of a missed dose.
Take your next recommended dose as soon as you can, but never “stack” your doses to make up for missed days.
Can I drink alcohol while on metformin?
Alcohol can have negative interactions with metformin, including an increased risk of low blood sugar (hypoglycemia). It is important to follow all guidelines and instructions on any prescription medications you take.
That said, with their doctor’s OK, many people do drink alcohol while taking metformin. Moderation is key.
General guidelines are the following: For women, a moderate amount of alcohol is no more than one drink per day, and for men, a moderate amount is no more than two drinks per day.
According to the National Institutes of Health, a drink is considered to be 12 ounces (oz) of regular beer, 5 oz of wine, or 1.5 oz of 80-proof distilled spirits.
Final thoughts
After 4 days, most people will have cleared metformin from their systems.
If you’re experiencing severe side effects from metformin, your symptoms should be alleviated after you’ve stopped taking the drug for those initial 96.8 hours.
There are no foods that you absolutely must avoid when taking metformin, but if nausea is making you want to avoid certain foods, this symptom should go away after 4 days without metformin.
If you’re taking metformin and choose to drink alcohol, it’s important to know that this can raise your risk of experiencing low blood sugar, particularly if you’re also using insulin.
If you are considering weaning off metformin completely, be sure to work with your doctor before adjusting your dose to minimize the risk of negative side effects like high blood sugar (hyperglycemia).
Suggested next article: Everything You Need to Know About Metformin.
