Metformin vs. insulin: Differences & similarities explained

In this article:

• Key differences
• Conditions treated
• Is metformin better than insulin?
• Cost & coverage
• Side effects
• Drug interactions
• Drug warnings
• Bottom line

In this article

• Key differences
• Conditions treated
• Is metformin better than insulin?
• Cost & coverage
• Side effects
• Drug interactions
• Drug warnings
• Bottom line

Diabetes mellitus, more commonly known as diabetes, is a health condition that affects millions of people and often requires medication to manage. Metformin and insulin are commonly prescribed medications to manage blood sugar levels in people with diabetes. In some cases, they may be used together. These drugs may help prevent diabetes complications like heart disease, kidney problems, and nerve damage.

Although both metformin and insulin help control diabetes, they have differences worth considering. For example, they have different approved uses, work in different ways, and have different side effects. They can also vary in dosage forms and costs. Read on to learn more about the similarities and differences between these medications. 

Metformin vs. insulin: Key differences

Metformin is an oral medication often used to treat Type 2 diabetes. It reduces glucose production in the liver and enhances the body’s response to insulin, improving insulin sensitivity. It’s mainly prescribed when lifestyle changes or other approaches don’t adequately control blood sugar levels. Metformin is available as regular tablets, extended-release tablets, and liquid solutions. It’s typically taken once or twice daily with a meal, depending on the dosage form.

Insulin therapy involves subcutaneous injections (under the skin) and is typically used to manage Type 1 diabetes. Insulin helps control blood sugar by allowing the sugar to enter the cells for energy. Different products contain various types of insulin, such as short-acting, intermediate-acting, and long-acting insulin, and they’re usually administered once daily or multiple times per day with meals. Insulin variants like Novolog and Humalog are fast-acting and work quickly, while other types may have a different onset of action.

Compare metformin vs. insulin key differences
	Metformin	Insulin
Drug class	Biguanide	Insulin
Brand/generic status	Brand and generic version available	Brand and generic version available
What is the brand name?	Glucophage, Riomet, Glumetza	Humalog, Novolog, Humulin R, Novolin R, Lantus, Levemir, Tresiba, Apidra, Toujeo, Basaglar
What form(s) does the drug come in?	Oral tablet, extended-release tablet, liquid oral solution	Multiple-dose vial, prefilled pen
What is the standard dosage?	Immediate-release: 500 mg twice daily or 850 mg once daily with meals Extended-release: 500–2000 mg once daily with an evening meal Dosage may be increased as needed and tolerated	Subcutaneous injection once or multiple times per day, depending on the type of insulin and dosage form  Dosage is adjusted based on individual needs and blood glucose levels
How long is the typical treatment?	Long-term	Long-term
Who typically uses the medication?	Adults and children 10 years and older	Adults, adolescents, children, and infants

 

Metformin vs. insulin: Conditions treated

Metformin is approved by the Food and Drug Administration (FDA) to manage Type 2 diabetes in adults and children ages 10 years and older. It’s often the first-line treatment for those with Type 2 diabetes due to its safety, effectiveness, and cost. Off-label uses may include the treatment of Type 1 diabetes (as add-on therapy to insulin) and polycystic ovary syndrome (PCOS). It may also sometimes be used for diabetes in pregnant women (gestational diabetes), weight management for overweight or obesity problems, and the prevention of diabetes in people with prediabetes.

Insulin, on the other hand, is approved for all types of diabetes. However, it’s typically used in individuals with Type 1 diabetes, as they can’t produce insulin naturally. It may be given to adults, children, and even infants of all ages. It is sometimes used in people with Type 2 diabetes when other medications aren’t enough to control glucose levels. Insulin is often considered for gestational diabetes, although healthcare providers often recommend starting with lifestyle changes. Insulin may be used if needed during pregnancy to protect both the mother and the baby.

While neither metformin nor insulin is a cure, they help prevent serious complications like heart disease, kidney disease, eye problems, nerve damage, and even amputation caused by unmanaged diabetes. 

Compare metformin vs. insulin conditions treated
Condition	Metformin	Insulin
Type 2 diabetes	Yes	Yes
Type 1 diabetes	Off-label	Yes
Prevention of Type 2 diabetes	Off-label	No
Gestational diabetes	Off-label	Yes
PCOS	Off-label	No
Weight management	Off-label	No
Weight gain from antipsychotic medication	Off-label	No

 

Is metformin better than insulin?

Metformin and insulin are both effective treatments that can improve glucose control in people with diabetes. The best option will depend on different factors, such as the type of diabetes being treated and other medications being taken. 

Metformin is often the first choice for Type 2 diabetes mellitus because it’s effective and carries a low risk of low blood sugar levels (hypoglycemia). On the other hand, insulin may be more useful for Type 1 diabetes in people who can’t produce insulin or in emergency situations in which high blood sugar levels (hyperglycemia) need to be rapidly controlled. 

The American Diabetes Association recommends metformin and insulin be used together in some cases. For example, people with Type 1 diabetes might take metformin to reduce the amount of insulin needed since it helps improve insulin action in the body. In people with Type 2 diabetes who are on metformin, insulin may be recommended if blood sugar levels remain high, HbA1c levels haven’t improved, or there are unexpected signs of weight loss.

It’s important to consult a healthcare provider on the most appropriate diabetes treatment options. A healthcare provider can help create a diabetes care plan to manage blood sugar levels. 

Metformin vs. insulin: Insurance coverage and cost comparison

Metformin is typically available as a low-cost generic medication. It’s often covered by most insurance and Medicare plans, making it accessible for many people. Insulin comes in brand-name and biosimilar versions, with coverage varying depending on the insurance plan. 

Metformin is generally more affordable, with prices being lower when purchased as a generic. Insulin, especially brand types like Humulin or Novolin, tends to be more expensive. Factors such as the type of insulin, the quantity, and the pharmacy used can greatly affect the total cost. 

Using a SingleCare prescription discount card can help you save on metformin and insulin, helping to reduce out-of-pocket expenses.

Compare metformin vs. insulin cost and coverage
	Metformin	Insulin
Typically covered by insurance?	Yes	Yes
Typically covered by Medicare Part D?	Yes	Yes
Quantity	60, 500 mg tablets	Varies by product
Average retail price	$165 for 60, 500 mg tablets	Varies by product
SingleCare cost	$3	Varies by product

 

Metformin vs. insulin: Side effects

Metformin and insulin can cause different side effects. Metformin is more likely than insulin to cause gastrointestinal problems, such as nausea, vomiting, diarrhea, and indigestion. The side effects of metformin are often temporary as the body adjusts to the medication and can often be reduced by taking metformin with food. 

Insulin is more likely than metformin monotherapy to cause hypoglycemia, which may be something to consider. Symptoms of hypoglycemia include shakiness, sweating, and confusion. Therefore, blood sugar levels generally need to be monitored closely while taking insulin. 

Metformin typically does not cause weight gain, which is an advantage over some antidiabetic medications. Instead, some people may experience weight loss. On the other hand, weight gain is a common side effect in people using insulin therapy. Because insulin is injected, it may also cause injection site reactions, such as irritation, redness, and swelling around the injection area.

Compare metformin vs. insulin side effects
	Metformin		Insulin
Side effect	Applicable?	Frequency	Applicable?	Frequency
Hypoglycemia	Yes	1–5%	Yes	N/A
Nausea or vomiting	Yes	26%	No	–
Diarrhea	Yes	53%	Yes	N/A
Indigestion	Yes	7%	No	–
Cold symptoms	Yes	1–5%	Yes	N/A
Injection site reactions	No	–	Yes	N/A
Edema	No	–	Yes	N/A
Itching	No	–	Yes	N/A
Weakness	Yes	9%	No	–
Weight gain	No	–	Yes	N/A

Frequency is not based on data from a head-to-head trial. This may not be a complete list of adverse effects that can occur. Please refer to your healthcare provider to learn more.

Source: DailyMed (Metformin), DailyMed (Insulin)

Metformin vs. insulin: Drug interactions

Metformin and insulin are commonly used to manage diabetes, but they can interact with other medications in ways that may affect blood sugar control. 

Taking metformin or insulin with sulfonylureas (like glipizide or glimepiride) or glinides (such as repaglinide or nateglinide) may increase the risk of hypoglycemia. Therefore, people using these combinations may need to be careful about their doses and monitor their blood sugar closely to avoid problems. 

On the other hand, some medications can raise blood sugar levels, making metformin and insulin less effective. Corticosteroids (like prednisone and dexamethasone), diuretics (such as hydrochlorothiazide and furosemide), and certain antipsychotics (such as olanzapine and clozapine) can all contribute to higher blood sugar. When taking these drugs, you may need to adjust your diabetes medications to maintain proper blood sugar levels. 

In addition, carbonic anhydrase inhibitors can increase the risk of a serious condition called lactic acidosis when used with metformin. Beta blockers can hide the signs of low blood sugar, making it harder for someone to notice when their blood sugar drops too low on metformin or insulin. 

Consult a healthcare provider about any medications you take, such as prescription drugs, over-the-counter medicines, and herbal supplements, before taking metformin or insulin. 

Compare metformin vs. insulin drug interactions
Drug	Drug class	Metformin	Insulin
Diamox (acetazolamide) Zonegran (zonisamide)	Carbonic anhydrase inhibitors	Yes	Yes
Humalog (insulin lispro) NovoLog (insulin aspart) Lantus (insulin glargine)	Insulin	Yes	Yes
Glucotrol (glipizide) Amaryl (glimepiride)	Sulfonylureas	Yes	Yes
Starlix (nateglinide) Prandin (repaglinide)	Glinides	Yes	Yes
Deltasone (prednisone) Orapred (prednisolone) Decadron (dexamethasone)	Corticosteroids	Yes	Yes
Lasix (furosemide) Microzide (hydrochlorothiazide) Aldactone (spironolactone)	Diuretics	Yes	Yes
Seroquel (quetiapine) Zyprexa (olanzapine)	Atypical antipsychotics	Yes	Yes
Lopressor (metoprolol) Inderal (propranolol) Tenormin (atenolol)	Beta blockers	Yes	Yes

Consult a healthcare professional for other possible drug interactions. 

Insulin vs. metformin: Drug warnings

Metformin and insulin may come with different warnings and precautions. Metformin can cause a serious condition called lactic acidosis, especially in people with kidney problems, liver disease, heavy alcohol use, or conditions like heart failure. Symptoms include severe fatigue, trouble breathing, stomach pain, and muscle cramps. 

Long-term use of metformin may also lead to vitamin B12 deficiency, causing anemia. In addition, metformin should be temporarily stopped before certain medical procedures that use contrast dye in order to avoid increasing the risk of kidney damage and lactic acidosis. While metformin alone doesn’t usually cause low blood sugar, the risk increases when combined with insulin or other diabetes medications.

On the other hand, insulin’s most common side effect is hypoglycemia, which can occur from skipping meals, overusing insulin, or exercising without adjusting the dose. Symptoms include sweating, shaking, confusion, and, in severe cases, unconsciousness or seizures. Repeated insulin injections in the same spot can also cause skin issues like lumps, thinning, or thickening, which may affect how insulin works. In addition, insulin can lower potassium levels, leading to muscle weakness or irregular heartbeat. 

Consult a healthcare provider for other potential warnings and precautions before starting insulin or metformin treatment.

Bottom line 

Metformin and insulin are key medications for glycemic control, but they work in different ways and serve different purposes. Metformin is often the first choice for people with Type 2 diabetes because it’s an easy-to-take pill that usually doesn’t cause low blood sugar. On the other hand, insulin is often needed in people with Type 1 diabetes as well as some people with Type 2 diabetes who need more help controlling their blood sugar. 

Both medications can help prevent serious health problems, like cardiovascular disease and nerve damage, but they can also cause some side effects. For example, metformin may cause stomach problems, while insulin can lead to low blood sugar levels. It’s important to talk to a healthcare provider to find the best treatment plan for your condition.