Metformin: 10 Things You Should Know
Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on April 18, 2021.
Metformin is a Workhorse for Type 2 Diabetes
Metformin, commonly known by other names such as:
has been available for the oral treatment of type 2 diabetes since 1995.
Metformin helps to control blood sugar (glucose) levels and is sometimes used in combination with insulin or other medications.
Metformin is a true workhorse for diabetics: a study published in Diabetes Care showed that the number of people who started metformin as their first treatment has increased since 2005. In fact, metformin is recommended in type 2 diabetes guidelines as the first-line drug treatment for new patients, along with diet and exercise.
Metformin is Truly Lifesaving
We know that starting type 2 diabetes treatment with metformin helps to prevent the need for additional diabetes medications in the long-term. But what else does it do?
A study from the Annals of Internal Medicine demonstrated that starting diabetes treatment with metformin is also linked with a lower long-term risk of:
- heart attack
- and death
than starting with a sulfonylurea, like glyburide or glipizide.
Metformin: An Affordable First-Line Medicine
A generic form of both regular-release and extended-release metformin is available at your pharmacy. It is very affordable, running less than $20 per month with online coupons. Prices will vary from city to city, and even pharmacy to pharmacy. Always check for coupons if you are paying cash.
There are several different strengths of metformin, too. It may be that instead of taking the 1,000 mg (milligram) tablet of metformin per dose you could take two 500 mg tablets and save money.
Always ask for the least costly version of generic metformin, as some generics may be more expensive.
If at any time you feel like you cannot afford your medications, have a frank discussion with your doctor or pharmacist to look at other options.
Free samples, discount coupons, and even a switch to a more affordable drug class may be possible.
Insulin Resistance and the A1C
There are many forces at work when a patient is diagnosed with type 2 diabetes.
Insulin resistance is one of them, where the hormone insulin is not used effectively and too much sugar is left in the blood. Metformin works to make the body's cells more sensitive to insulin and decreases the amount of sugar naturally produced in the liver.
Guidelines from the American Diabetes Association (ADA) state that blood sugar levels should be targeted to the individual patient. Blood glucose targets (A1C) are individualized based on:
- duration of diabetes
- age/life expectancy
- comorbid conditions
- known CVD or advanced microvascular complications
- hypoglycemia unawareness
- individual patient considerations.
While metformin is a recommended as a first-line medicine, some patients may need to be started on a second drug at the same time to reach blood sugar goals.
The American Diabetes Association (ADA) suggests that the A1C measurement should be less than 7% for most nonpregnant adults with diabetes. However, more or less stringent glycemic goals may be appropriate for each individual. A1C goals may be slightly increased (for example, less than 8% or higher) for patients with history of severe hypoglycemia, other significant health conditions, if life-expectancy is limited, or in very young or much older patients.
In March 2018, the American College of Physicians (ACP) relaxed their recommendations on target A1C levels, suggesting that A1C should be between 7 and 8 percent for most adults with type 2 diabetes. For adults who achieve an A1C below 6.5 percent, the group suggests stepping down diabetes treatment to keep that level from going even lower.
Can't You Smell That Smell?
Pharmacists and patients are well aware that metformin may come with a fishy smell when you open the bottle. The smell does not mean the drug is spoiled, it's just due to it's inherent characteristics.
Metformin is associated with relatively few side effects, but nausea may be one of them, possibly due to this 'fishy' odor.
According to a report published in the Annals of Internal Medicine, some extended-release forms of metformin have a lower odor, and may be less likely to cause nausea. If you can't tolerate your metformin, let your doctor know. A switch to the extended-release form or a different manufacturer may do the trick.
Hypoglycemia: A Smaller Risk, But Still There
Hypoglycemia, or excessively low blood sugar, can occur due to the use of many diabetes medications.
One advantage of metformin is its low risk of causing hypoglycemia in only about 1% to 10% of patients. However, if someone has not eaten adequately, plays in strenuous sports without eating, or is also taking other other glucose-lowering agents such as sulfonylureas or insulin, hypoglycemia can set in.
Drinking alcohol with metformin can also lead to low blood sugar. Elderly or malnourished patients, and those with adrenal or pituitary insufficiency are especially at risk for low blood sugar.
Lactic Acidosis: A Rare But Serious Side Effect
A serious side effect called 'lactic acidosis' is listed in the patient education sheet for metformin. It's important you know about it, but it's also a rare side effect. Lactic acidosis is a medical emergency and must be treated in a hospital.
Lactic acidosis is a build-up of lactic acid in your blood due to low oxygen levels. Lactic acidosis can occur in people with kidney disease, heart disease, liver disease, if you drink excessive alcohol, are dehydrated and other risk factors, such as age over 65 years or a past history of lactic acidosis during metformin therapy.
Do not take metformin if you: have severe kidney problems, are allergic to metformin HCl or have a condition called metabolic acidosis including diabetic ketoacidosis (high levels of certain acids called “ketones” in your blood or urine).
What Are the Signs of Lactic Acidosis?
If you notice any of these signs, stop taking metformin and call your doctor right away.
Signs of lactic acidosis include:
- Feeling very weak or tired
- Unusual muscle pain or weakness
- Have unusual sleepiness or sleep longer than usual
- Trouble breathing
- Stomach discomfort, nausea, vomiting
- Feeling cold, especially in your arms and legs
- Feeling dizzy or lightheaded
- Have unexplained stomach or intestinal problems with nausea and vomiting or diarrhea
- Suddenly developing a slow or irregular heartbeat
Certain metformin drug interactions may increase your risk of lactic acidosis, so be sure to tell your doctor and pharmacists about all of the prescription medicines, herbal, vitamin or other over-the-counter (OTC) medicines you take.
Will Metformin Help Me Lose Weight?
Many people with type 2 diabetes have insulin resistance and need to lose weight. Of course, for anyone as directed by their doctor, the best way to lose weight is gradually through a combination of a healthy diet and daily exercise, along with required medications.
Large studies have looked at weight loss in patients taking metformin, and weight loss is variable.
- In some studies reported by the manufacturer, patients have lost up to 8.4 lbs., while in other studies, is was reported as a loss of 1.4 lbs.
- However, weight loss does seem to be the norm, even if it's only a slight weight loss, in contrast to the weight gain that often occurs with insulin or sulfonylurea treatment.
In general, while metformin is a useful drug to control blood sugar in diabetes, weight loss due to metformin may not enough. Patients should also use an appropriate diet and regular exercise for weight control in type 2 diabetes, as recommended by your doctor.
How Should I Take Metformin?
Metformin comes in a regular-release and extended-release tablets in varying strengths. Metformin is usually taken with a meal. It may be taken twice a day, but some forms of metformin are taken only once daily. Take your medicine at the same time each day as directed by your doctor.
It is also approved to be used in children 10 years of age and older with type 2 diabetes to improve blood sugar control in conjunction with an appropriate diet and regular exercise.
Metformin can cause stomach upset or stomach pain, heartburn, nausea or diarrhea at the beginning of treatment, but for many people these effects will subside over time.
- Taking with a meal can help to minimize stomach upset and diarrhea.
- To also help lessen these reactions and determine the most effective dose, your doctor will start you on a low dose and gradually increase it over time.
Low vitamin B12 in your blood (vitamin B12 deficiency) can occur. This may be more likely if you have had low vitamin B12 levels before. Your healthcare provider may do blood tests to check your vitamin B12 levels.
Talk to your doctor about all important side effects before you start treatment, as this is not a complete list.
Related: Metformin side effects (in more detail)
Finished: Metformin: 10 Things You Should Know
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- Umeda T, Minami T, Bartolomei K, et al. Metformin-Associated Lactic Acidosis: A Case Report. Drug Saf Case Rep. 2018 Feb 9;5(1):8. doi: 10.1007/s40800-018-0076-1. Accessed April 18, 2021.
- Salpeter SR, Greyber E, Pasternak GA, et al. Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes mellitus. Cochrane Database Syst Rev. 2010 Apr 14;(4):CD002967. Accessed April 18, 2021.
- American Diabetes Association. Checking Your Blood Glucose. Accessed April 18, 2021 at https://www.diabetes.org/diabetes/medication-management/blood-glucose-testing-and-control/checking-your-blood-glucose
- Knowler W, Fowler S, Hamman R, et al. Diabetes Prevention Program Research Group 10-year follow-up of diabetes incidence and weight loss. Diabetes Prevention Program Outcomes Study. Lancet. 2009;374:1677-1686. Abstract. Accessed April 26, 2017.
- Roumie C., Hung A., Greevy R., Grijalva C., Liu X., Murff H., Elasy T., Griffin M.; Comparative Effectiveness of Sulfonylurea and Metformin Monotherapy on Cardiovascular Events in Type 2 Diabetes Mellitus: A Cohort Study. Ann Intern Med. 2012;157:601-610. doi: 10.7326/0003-4819-157-9-201211060-00003 Accessed April 18, 2021
- Diabetes Prevention Program Research Group. Long-term safety, tolerability, and weight loss associated with metformin in the Diabetes Prevention Program Outcomes Study. Diabetes Care. 2012;35:731-737. Abstract. Accessed April 14, 2019.
- Domecq J, Prutsky G, Leppin A, et al. Clinical review: Drugs commonly associated with weight change: a systematic review and meta-analysis. J Clin Endocrinol Metab. 2015;100:363-70. Accessed April 18, 2021.