Januvia vs Metformin: Comparison of Diabetes Drugs

Published February 24th, 2021 by Erik Rivera
Fact Checked by
Camille Freking
Medically Reviewed:
Dr. Gerardo Sison
Updated Date: Mar 13th, 2021

An estimated 31 million people in the United States are affected by a condition called type 2 diabetes mellitus, in which the body is resistant to the effects of a hormone called insulin. Left unchecked, type 2 diabetes can cause serious and potentially fatal consequences. Two popular oral prescription medications for the treatment of type 2 diabetes include Januvia and metformin. Both drugs can effectively treat type 2 diabetes and control high blood sugar, but when comparing Januvia vs metformin, how do the medications stack up?


Metformin and Januvia are two popular medications that are most commonly associated with the treatment of type 2 diabetes. Metformin is a generic drug that is sold by a variety of manufacturers under different brand names, while Januvia is a brand name drug that is not available in a generic form and is manufactured solely by Merck. 

Metformin belongs to a class of drugs called biguanides and has become the most popular drug for the treatment of type 2 diabetes in the world since it was approved by the U.S. Food and Drug Administration (FDA) in 1995. Metformin is available in immediate-release and extended-release forms. Januvia was first approved by the FDA in 2006 and belongs to a class of drugs called dipeptidyl peptidase-4 (DPP-4) inhibitors. Januvia is only available in a standard formula and is intended to be used in conjunction with a healthy diet and exercise in order to manage high blood sugar.

Conditions Treated

Januvia and metformin are both FDA-approved for the treatment of type 2 diabetes. Additionally, metformin can also be used to treat polycystic ovary syndrome (PCOS) and can help manage weight gain caused by medications used to treat psychosis.

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Type 2 Diabetes

Type 2 diabetes is a medical condition in which patients do not properly regulate and use glucose, or sugar, for fuel in the body. Unlike type 1 diabetes, where diabetics cannot produce insulin, type 2 diabetics don't respond as well as they should to insulin and later in life can stop making enough. Type 2 diabetes condition occurs as a result of insulin resistance, which means that the body does not properly respond to the effects of a hormone called insulin that regulates the levels of glucose in the blood. When people with type 2 diabetes do not manage their condition properly, uncontrolled high blood sugar causes disorders in the nervous, immune, and circulatory systems. Serious conditions and complications associated with high blood glucose include:

  • Nerve damage in the feet and hands (neuropathy)
  • Increased risk of heart problems like heart failure and heart attack
  • Increased risk of kidney disease
  • Hyperglycemia
  • Cognitive impairment
  • Diabetic ketoacidosis
  • Weight gain
  • Damage to the blood vessels of the eyes (retinopathy)

Polycystic ovary syndrome

Polycystic ovary syndrome, commonly referred to as PCOS, is a common hormonal disorder that is estimated to affect anywhere from 6 to 12 percent of women in the United States. In addition to being one of the leading causes of infertility, PCOS is associated with a number of other symptoms, including insulin resistance, higher levels of male hormones, acne, irregular periods, thinning scalp hair, and the growth of excess body hair. Because many women with PCOS are insulin resistant, metformin is sometimes prescribed to treat the condition. Metformin helps to balance the levels of insulin in the body, lower blood glucose levels and minimizing other metabolic effects caused by PCOS.


One of the biggest differences between Januvia and metformin is the cost of the drugs. Januvia is extremely expensive and unaffordable for most patients, while metformin is covered by most types of insurance and is affordable for most people.

Januvia is extremely expensive, with a prescription of 30 pills at a strength of 100 mg costing approximately 500 dollars. Despite the fact that many people with type 2 diabetes cannot afford Janucia, the drug remains the most popular gliptin medication for the treatment of type 2 diabetes. One of the drivers for the high cost of Januvia is the fact that no generic form of the drug exists. The original manufacturer, Merck, holds an exclusive patent on Januvia that is not set to expire until 2026. Following expiration of the original manufacturer’s patent, a generic version of the drug will be able to enter the market following FDA approval. The price of Januvia rose 93 percent between 2010 and 2015 as a result of the popularity of the medication, the prevalence of type 2 diabetes in the United States, and the lack of a generic alternative. 

By contrast, metformin is highly affordable and is covered by most forms of health insurance. Metformin is available in a brand name form produced by several different manufacturers and is also available as a generic drug. A prescription of 30 tablets at a strength of 1000 mg costs approximately 15 dollars, making the drug much more accessible for patients with type 2 diabetes. Metformin can be considered safe during breastfeeding.

Side Effects


Januvia can cause a wide range of side effects. The most common side effects associated with Januvia include:

  • Upper respiratory infection
  • Stuffy or runny nose
  • Sore throat
  • Headache

Serious side effects associated with Januvia include:

  • Low blood sugar (hypoglycemia) as evidenced by:
    • Headache
    • Irritability 
    • Dizziness
    • Sweating
    • Weakness
    • Drowsiness
    • Hunger
    • Confusion
    • Feeling jittery
    • Fast heart beat
  • Serious allergic reactions
  • Kidney problems, including possible need for dialysis
  • Joint pain, including potentially severe joint pain
  • Skin reactions such as blisters or breakdown of the outer layer of the skin

Rare and potentially life-threatening side effects of Januvia have also been known to occur. These side effects include:

  • Pancreatitis (inflammation of the pancreas), particularly in patients who have a history of pancreatitis, gallstones, a history of alcoholism, high blood triglyceride levels, or kidney problems
  • Heart failure, particularly in patients who have had previous heart problems or kidney problems. Signs of heart failure may include:
    • Difficulty breathing, especially when lying down
    • Shortness of breath
    • Unusually quick weight gain
    • Swelling or fluid retention
    • Unusual tiredness
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Common side effects associated with metformin that usually do not require medical attention include:

  • Gas
  • Weight loss
  • Diarrhea
  • Bloating not from weight gain
  • Heartburn
  • Headache
  • Constipation
  • Stomach pain
  • Nausea or vomiting
  • Unpleasant metallic taste in the mouth

Most patients using metformin will only experience mild side effects of the medication. However, metformin is also associated with some serious side effects that occur rarely but require medical attention. The most serious side effects associated with metformin are lactic acidosis, hypoglycemia, and anemia.

Lactic acidosis is a medical condition that occurs as a result of an imbalance of lactic acid in the body, which causes a pH imbalance. When left untreated, lactic acidosis can be fatal, but as long as the condition is detected early, it can be treated. When metformin builds up in the blood, it can contribute to an increased risk of experiencing lactic acidosis. Patients who are most at risk of experiencing lactic acidosis include those who use alcohol excessively, have kidney disease or kidney problems, liver problems, heart problems including acute heart failure, surgery or radiology procedures using iodine contrast, and recent heart attack.  Symptoms of lactic acidosis include:

  • Feeling cold
  • Stomach pain with any of these symptoms
  • Dizziness
  • Extreme fatigue
  • Muscle pain
  • Flushing or sudden reddening and warmth of the skin
  • Vomiting
  • Trouble breathing
  • Nausea
  • Fast or slow heart rate
  • Weakness
  • Decreased appetite
  • Lightheadedness

Anemia is a medical condition that occurs when red blood cells in the body are unable to carry a sufficient amount of oxygen to the different organs and tissues. Metformin can increase a person’s risk of experiencing anemia by reducing the level of vitamin B-12 in the body, as vitamin B-12 deficiency can contribute to anemia. Common symptoms of anemia include:

  • Lightheadedness
  • Dizziness
  • Tiredness

Metformin can also cause low blood sugar, also known as hypoglycemia, in patients who  have a poor diet,  drink alcohol to excess, take other diabetes medications, or exercise strenuously. Symptoms of hypoglycemia include:

  • Stomach pain
  • Lightheadedness
  • Weakness
  • Nausea
  • Vomiting
  • Dizziness
  • Tiredness
  • Abnormally fast or slow heartbeat

Patients taking metformin are most likely to experience diarrhea, nausea, and vomiting as side effects. The side effects of metformin are usually at their worst when a patient first starts taking the medication, and they commonly decrease as the patient’s body adjusts to the drug. However, some patients find the side effects of metformin intolerable and stop taking the drug before their bodies have a chance to adapt to the medication. Side effects of metformin are more likely to be experienced when patients use the immediate-release form of the drug. In order to reduce their chance of experiencing side effects, patients using metformin should take the drug with a meal.


Januvia and metformin are both effective drugs that are used to help manage blood sugar levels in patients with type 2 diabetes. Although both drugs can cause serious side effects, there are fewer side effects associated with Januvia and the drug is better tolerated than metformin. Januvia is not available in a generic form and is considerably more expensive, while metformin is affordable for most patients. Seek medical advice from a healthcare professional to determine which diabetes medicine is right for you. Patients can save on whichever type 2 diabetes prescription drug they use with a pharmacy discount card from USA Rx, which can help make your prescription more affordable.


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