People who take metformin for diabetes management will often take the medication once or twice per day.
In some cases, however, people may take slow-release metformin tablets, 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.
Why know how long metformin stays in your system?
Taking daily medication can be difficult. Life can sometimes get in the way of taking our medications as prescribed and on time.
Metformin is best taken once or twice daily (however always check with your doctor first), but this can create confusion if you’re trying to amp up or lower your dose, or if you’re trying to wean yourself off the medication altogether.
Alternatively, it is helpful to know how long it lasts in your system if you’ve forgotten to take your medication, or if you are wondering when it is safe to take your next full dose, or if the metformin that you’ve previously taken will negatively 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.
Read more: Signs Metformin Is Working (Or Isn’t Working)
An improper build-up of metformin in the system can happen if your kidneys are not properly functioning to process the medication. This can result in a condition called lactic acidosis, which can be life-threatening.
Contact your doctor if you’re experiencing symptoms of lactic acidosis that include:
- Feeling disoriented
- Rapid breathing
- Rapid heart rate
- Abdominal pain
- Lethargy and fatigue
- Muscle cramps and muscle pain
- Body weakness
- Reduced appetite
- Yellowing of the skin or eyes
Some of these symptoms can be confused with normal metformin side effects, but be discerning if you start to experience any new symptoms after you’ve been on metformin for a while.
Typically, side effects of metformin, such as vomiting, diarrhea, and nausea, go away after a few weeks on the medication.
All this being said, metformin is generally a very safe drug and most people experience minimal side effects.
For those who experience significant side effects, there are good alternatives to metformin, including several metformin combination drugs that may have fewer side effects.
What is the half-life of metformin?
The half-life of a medication is the time it takes for 50% 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.
The average elimination half-life of metformin in plasma 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% less potent. 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’s bodies are different. There are some special populations where metformin will stay in their bodies longer.
People with renal impairment
For people living with kidney disease or kidney failure, metformin will stay in the body much longer.
For people who take metformin who have mild and moderate kidney failure, the oral and renal clearance of metformin is decreased by 33% and 50%, and 16% and 53%, respectively.
Older people tend to have metformin stay in their system longer than younger people who take metformin. 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 initiated in patients who are 80 years and older unless measured creatinine clearance can show that renal function is not reduced.
People who have a slower metabolic rate will have metformin in their system for longer. This is because your body is processing everything (including food, alcohol, and medications) more slowly.
Compared to healthy, non-diabetic individuals, people who take metformin with type 2 diabetes will have the medication in their system for longer, even after stopping the drug.
Your 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 half-life as well.
If you’re on a low dose of metformin, the half-life is smaller than someone who is on the maximum daily dose of metformin, which is ~2,550 mg per day.
If you’re taking the maximum dose, expect the medication to stay in your system much longer than someone else who may only be taking 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’s effects may stay in your system longer than someone who took the medication for one week and then stopped taking it.
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 metformin stay in your system?
After you’ve completely stopped taking metformin, it will stay in your system for approximately 96.8 hours or almost 4 days.
It takes approximately 5.5 x 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) 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 it will have a negligible amount left in your system.
Metformin is active in the following systems after completely stopping the medication:
- Blood: 96.8 hours
- Saliva: ~96 hours
- Urine: Between 1-4 days, depending on hydration
Frequently asked questions
Metformin can negatively interact with other prescribed medications, so always tell your doctor all medications you currently take if you’ve recently been prescribed metformin, or if you’re on metformin, make sure you tell your doctor before starting any new medications.
Metformin can interact with insulin, sulfonylureas, and meglitinides. It may also interact with diuretics, steroids, and corticosteroids.
It can sometimes interact with substances that increase the risk of lactic acidosis, which can be fatal.
Your doctor may want you to completely be weaned off metformin before starting another drug.
Metformin will be active in your body for 4 days, but you may notice higher blood sugar levels within a day or two 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.
Alcohol can have negative interactions with metformin, including an increased risk of low blood sugar.
Follow all guidelines and instructions on any prescription medication, and act accordingly.
Many people, however, 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.
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 after those initial 96.8 hours.
Additionally, if many people drink moderate amounts of alcohol while taking metformin, so you do not need to clear it completely from your system before drinking alcohol.
However, you should be aware of the increased risk of hypoglycemia (low blood sugar) when you drink alcohol if you take metformin, especially if you’re also on insulin.
There are no foods that you absolutely must avoid when taking metformin, but if nausea is causing food aversions, they should go away after this timeframe as well.
As for weaning off metformin completely, always work with your doctor before lowering or completely stopping your dose to help avoid negative side effects like high blood sugar.
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