Metformin Side Effects

Metformin is a drug that is used in the treatment of type 2 diabetes and sometimes to treat women with PCOS, it is taken orally and is most commonly prescribed to patients that are overweight, obese or those that still have a healthy kidney function. While the side effects of metformin are luckily fairly limited there are still quite a few adverse effects that can plague the recipients. As always, contact your doctor or a health care professional when dealing with any health related issue. Here is a list as below:

Metformin Side Effects List

metformin side effects
  • Trouble breathing
  • Stomach pain, including nausea and vomiting
  • Irregular heart rate
  • Shortness of breath
  • Blurry vision
  • Seizures
  • Chest pain
  • Confusion
  • Weakness or fatigue
  • Headaches
  • Diarrhea
  • Bloating due to gas buildup
  • Low blood sugar or high blood sugar
  • Sudden weight loss or gain

General Causes of Metformin Side Effects:

Lactic Acidosis:

This is potentially the most serious of the metformin side effects. The uptake of lactate by the liver is effected by metformin in a negative way. If the kidneys do not process the excess lactate the blood of the patient will acidify which can lead to a whole slew of problems. Most of which are similar to the feeling one gets after an intense workout. For example: anxiety, hyperventilation, irregular heart rate nausea and in some cases vomiting. This is the reason that metformin is generally only prescribed to people with a healthy kidney function. This side effect is potentially lethal and when you experience any of the symptoms you should immediately contact your doctor or a local hospital. Complications do occur when dealing with these problems, but are fairly rare. The rate of fatalities is reported to be around 1 in 1000 over a 10 year period. While this may seems significant, it still pales to the likely rate of fatality that untreated type 2 diabetes patients would face, which according to various sources lies in the range of 50 per 1000 patients over a ten year period.

Gastrointestinal problems

The most common negative effects for taking metformin. Clinical trials show that as much as 50% of the patients prescribed metformin are affected by this type of problems. While this is not the most serious adverse reaction it can still cause extreme discomfort. These are some of the symptoms of gastrointestinal discomfort: nausea, cramps, vomiting, diarrhea and it is often accompanied by flatulence. Fortunately these negative effects are most common when the drug is first prescribed or when the dosage is changed. For this reason the starting dose is often fairly low and will slowly be increased to the required levels. This way the body of the patient has the time to react to the changing circumstances. Once the patient is used to the required dose they are unlikely to keep experiencing these adverse effects. However, one problem that can manifest itself after prolonged usage of metformin is that B12 can no longer be properly absorbed. This will lead to a B12 deficiency and a close eye needs to be kept on long term patients for this reason. A prolonged B12 deficiency can cause damage to the nerve system. The symptoms will usually only manifest themselves after a decade and in some cases even longer. By that time the damage can already be irreversible. As a B12 deficiency is often hard to detect, usually preventative measures are taken to avoid this fairly serious side effect.

Allergic reactions

headache a side effect of metformin

There have been a number of cases where patients have experienced an allergic reaction to metformin. It is extremely important to check for an allergic reaction as it requires emergency treatment. So keep the following symptoms in mind when starting a metformin treatment: Trouble breathing, hives and/or swelling in the face, particularly the lips, tongue or throat.


While certainly a serious matter a metformin overdose is not extremely dangerous. Accidental overdoses are unlikely to have serious repercussions, though the risk is higher for the elderly and children. Fatalities are quite rare, but they unfortunately still occur. Intentional overdoses are most likely to result in death, however survivors have been reported even for the most extreme cases of overdoses. So this metformin side effect is fairly mild when compared to other prescription drugs. The signs of an overdose are usually simply a worse case of the regular metformin side effects. The most serious of which is, as mentioned before, lactic acidosis. This potentially life-threatening complication will need to be treated as soon as possible, as there is not antidote the procedures usually aim to strengthen the general health of the patient. In serious cases where this is not enough blood transfusion and dialysis can be utilized to directly influence the acidity of the blood.

General Advice When Dealing With the Side Effects of Metformin

As you can see there are still quite a few serious negative effects of metformin that can have an effect on the lives of its users. However, almost all of these are not life threatening, with the exception of lactic acidosis. When proper care is taken to slowly build up the dose of the drug one should only experience mild discomfort, unless there are underlying health issues, such as a reduced kidney function. For this reason, among others, you should never increase the dose by yourself, but always contact the health professional that prescribed you the medication.

Disclaimer: We strive to give the most up to date and accurate information on metformin side effects, however the accuracy cannot be guaranteed. This information should only be used for educational purposes and is in no way a substitute for the expertise and judgment of a healthcare professional. This article is in no way intended to cover all potential uses and adverse effects. If you have any health related questions, or questions about metformin in particular you should immediately contact your health practitioner. Side effects, particularly unknown ones should be reported to the FDA.