People taking metformin to treat diabetes often take the drug once or twice a day.
However, in some cases, people can take slow-release metformin tablets, which can be taken less frequently.
This is usually simple. However, it’s important to know how long metformin stays in your system for a variety of reasons.
In this article, we will explore how long a drug is active in your body after you have taken it or stopped taking it.
How do you know how long metformin stays in your system?
Taking your medication on a daily basis 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 a day (however, always check with your doctor first), but it can cause confusion if you’re trying to increase or decrease your dose or go off the medication altogether.
Alternatively, it’s worth knowing how long it stays in your system if you’ve forgotten to take a medicine, or are wondering when it’s safe to take your next full dose, or if the metformin you’ve been taking will negatively interact with other medications or food or alcohol you plan to consume .
Does metformin take time to build up in your system?
Yes, and if you’ve just started taking metformin, you won’t see an immediate improvement in your blood sugar or weight loss.
The first effects on blood sugar levels can be seen within 48 hours of starting the drug, but the most significant effects will only be seen after 4-5 days of consistent use of the drug.
However, achieving any weight loss expectations can take weeks or months and will also require changes in diet and exercise.
Read more: Signs that metformin is working (or not working)
Improper metformin buildup in the system can happen if your kidneys are not functioning properly to process the drug. This can cause a condition called lactic acidosis, which can be life threatening.
Call your doctor if you have symptoms of lactic acidosis that include:
- Feeling disoriented
- Rapid breathing
- Fast heart rate
- Lethargy and fatigue
- Muscle cramps and muscle pain
- Body weakness
- Decreased appetite
- Yellowing of the skin or eyes
Some of these symptoms may be mistaken for the normal side effects of metformin, but care should be taken if you experience any new symptoms after using metformin for some time.
Typically, metformin side effects such as vomiting, diarrhea and nausea go away after a few weeks of use.
All things considered, 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 drug is the time it takes for 50% of the drug’s active ingredient to be metabolized or eliminated from the body. The elimination half-life of metformin from red blood cells is approximately 17.6 hours.
The mean plasma elimination half-life of metformin is only 6.2 hours, but most of metformin’s active ingredients accumulate in red blood cells (RBCs), so that’s where we’ll focus.
This means that every 17.6 hours the drug becomes 50% weaker. However, there are some caveats.
Does metformin stay in some people’s bodies longer than others?
Yes. The half-life of metformin is not an exact science as every body is different. There are special populations where metformin stays in the body longer.
People with impaired kidney function
For people living with kidney disease or kidney failure, metformin will stay in the body much longer.
In people taking metformin with mild and moderate renal impairment, the oral and renal clearance of metformin are reduced by 33% and 50% and 16% and 53%, respectively.
Older people tend to have metformin in their system longer than younger people who take metformin. There are several reasons for this, but the main one is decreased kidney function in older people with diabetes.
For this reason, it is recommended that metformin treatment is not initiated in patients 80 years of age and older, unless renal function is not impaired by measurement of creatinine clearance.
People who have a slower metabolic rate will have metformin in their system longer. This is because your body processes everything (including food, alcohol, and medications) more slowly.
Compared to healthy people without diabetes, people taking metformin with type 2 diabetes will have the drug in their system for longer, even after stopping the drug.
your body weight
The greater your body weight, the longer metformin will stay in your body. This applies to all drugs.
The higher your body weight, the more likely you are to take a higher dose of metformin, which will also affect the half-life.
If you take a low dose of metformin, the half-life is shorter than for someone taking the maximum daily dose of metformin, which is ~2550 mg per day.
If you are taking the maximum dose, expect the drug to stay in your system much longer than someone else who may only be taking 500mg per day.
How long have you been taking the drug?
If you’ve been taking metformin for 10 years and stop taking it, the effects of the drug may last longer in your system than someone who took the drug for a week and then stopped.
While medications build up in your system, they take some time to break down, even if you’re not actively taking them.
How long does metformin stay in your body?
Once you stop taking metformin completely, it will stay in your system for approximately 96.8 hours or nearly 4 days.
It takes approximately 5.5 times the elimination half-life for metformin to be completely eliminated from the body, which is:
5.5 x 17.6 hours = 96.8 hours
That said, it’s perfectly fine (and expected) to take a metformin dose more often than every 4 days, but that’s how long it would take to clear it completely from your body if your kidneys were working properly.
Different body systems may clear metformin faster than others, but a negligible amount will remain in the body over the course of 4 days.
Metformin is active in the following systems after complete discontinuation of the drug:
- Blood: 96.8 hours
- Saliva: ~96 hours
- Urine: 1 to 4 days, depending on hydration
Frequently asked questions
Metformin may interact negatively with other prescribed medications, so always tell your doctor about all the medications you are currently taking, if you have recently been prescribed metformin, or if you are taking metformin, be sure to tell your doctor before starting any new medications.
Metformin may 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 come off metformin completely before starting another medication.
Metformin will be active in your body for 4 days, but you may notice higher blood sugar within a day or two of missing a dose.
Take the next recommended dose as soon as possible, but never “stack up” 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 for any prescription drugs and follow them.
However, many people drink alcohol while taking metformin. Moderation is key.
The general guidelines are as follows: 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 clear the metformin from the body.
If you are experiencing severe metformin side effects, your symptoms should resolve when you stop taking the drug after these initial 96.8 hours.
Additionally, if many people drink moderate amounts of alcohol while taking metformin, so you don’t need to completely remove it from your body before drinking alcohol.
However, be aware of the increased risk of hypoglycaemia (low blood sugar) when drinking alcohol when taking metformin, especially if you are also taking insulin.
There are no foods you should absolutely avoid while taking metformin, but if nausea causes you to not want to eat, it should also subside after this time.
When it comes to stopping metformin completely, always work with your doctor before lowering or stopping your dose altogether to avoid negative side effects such as high blood sugar.
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