The commonly prescribed drug is regularly dispensed to patients tackling type 2 diabetes
The NHS has a word of warning on its website for anyone who is taking metformin, though it is especially aimed at people who are taking the commonly prescribed pill for a long time. Metformin is a medication prescribed for the treatment of type 2 diabetes and gestational diabetes.
It is commonly used to help prevent type 2 diabetes in people who are at a heightened risk of developing the condition. Type 2 diabetes occurs when the body either does not produce sufficient insulin or the insulin produced is ineffective. This can lead to high blood sugar levels, a condition known as hyperglycaemia.
Metformin works by lowering blood sugar levels through enhancing the body’s insulin sensitivity. Typically, it is recommended for diabetes when lifestyle changes such as diet and exercise have proven insufficient in managing blood sugar levels.
According to the latest statistics, metformin is the most commonly prescribed drug for the treatment of type 2 diabetes in England. In 2024, approximately 26.4 million metformin hydrochloride treatments were dispensed. The drug is available by prescription in various forms, including tablets, a liquid solution for swallowing, and sachets of powder that can be dissolved in a beverage.
Diabetes treatment typically lasts a lifetime. However, if your kidneys are not functioning correctly, your doctor will advise you to stop taking metformin and transition to an alternative medication. It is crucial not to stop taking metformin without consulting your doctor. Abruptly halting metformin can lead to increased blood sugar levels and a deterioration of your diabetes
Common side effects
As with any medication, metformin may lead to side effects, but not everyone experiences them. These typical side effects occur in over one in 100 people. There are strategies you can employ to manage them:
- Feeling sick (nausea).
- Being sick (vomiting).
- Diarrhoea.
- Stomach ache.
- Loss of appetite.
- A metallic taste in the mouth.
NHS vitamin warning
Besides all of the side effects mentioned above, there is one particular issue that people who take metformin may face that can lead to other health problems. The NHS has issued a warning about this online, which reads: “Taking metformin can cause vitamin B12 deficiency if you take it for a long time.”
It adds: “This can make you feel very tired, breathless and faint, so your doctor may check the vitamin B12 level in your blood. If your vitamin B12 levels become too low, vitamin B12 supplements will help.” Call your doctor or call 111 straight away if you:
- Feel very tired.
- Have muscle weakness.
- Have a sore, red tongue.
- Have mouth ulcers.
- Have problems with your vision.
- Have pale or yellow skin (this may be less obvious on brown or black skin).
Vitamin B12: Why it’s important and the symptoms to look out for if you’re deficient
Why is a vitamin B12 deficiency bad?
Vitamin B12 deficiency can cause a range of symptoms that may be subtle at first. Tell your doctor if you experience:
- Extreme fatigue.
- Tingling, numbness, or “pins and needles” in your hands and feet.
- A sore and red tongue.
- Pale or yellow skin.
- Mood changes, including irritability or depression.
- Memory problems or cognitive impairment.
Vitamin B12 helps maintain a healthy nervous system; a lack of it can result in nerve damage, which may cause sensations of numbness and tingling in the extremities. The symptoms can vary widely, from memory issues and difficulty concentrating to severe confusion, dementia, and in extreme cases, psychosis.
A B12 deficiency can also impair physical coordination, potentially resulting in balance problems and problems with walking. If not addressed, the neurological damage may become permanent. During pregnancy, a B12 deficiency raises the risk of neural tube defects, such as spina bifida, in the developing baby. Severe B12 deficiency can also lead to temporary infertility.
Vitamin B12 is also necessary for folate, which is essential for producing DNA and healthy red blood cells. Insufficient B12 disrupts healthy DNA cells, leading to anaemia. Anaemia can cause fatigue, pale skin, shortness of breath, and headaches. Some research indicates a potential connection between B12 deficiency and a heightened risk of coronary artery disease and stroke, too.
How to avoid B12 deficiency when taking metformin?
According to a National Institutes of Health study, people taking metformin should undergo annual testing for vitamin B12 deficiency. The study’s statement reads: “In case of vitamin B12 deficiency, early replacement with intramuscular vitamin B12 to restore hepatic storage of vitamin B12 is recommended.”
The American Diabetes Association advises that patients on metformin should undergo annual B12 testing, especially those who are at an increased risk for deficiency or exhibit symptoms like anemia or neuropathy. Research indicates that the likelihood of deficiency rises with higher dosages (exceeding 1,500 mg daily) and extended treatment periods (lasting more than four to five years).
If you have additional risk factors, such as being over 65, following a vegan diet, or taking proton pump inhibitors for acid reflux, you might require more frequent testing. To enhance your vitamin B12 levels, consider incorporating foods that are high in this nutrient, including meat (particularly beef), poultry, fish (like salmon and cod), eggs, dairy products, and fortified foods.
The benefits of metformin for managing diabetes are great. You shouldn’t ever stop taking your medication without first speaking to your doctor, they can determine the best course of action for managing both your diabetes and your B12 levels.