Metformin vs Janumet

Metformin vs. Janumet

Metformin is an oral medication that lowers blood glucose by influencing insulin sensitivity. It is used to treat type 2 diabetes, and it works by increasing the sensitivity of various tissues to insulin. This reduces the level of sugar in the blood and can help prevent complications of diabetes such as heart disease, blindness, and kidney disease. Metformin can also be used to treat polycystic ovaries and weight gain caused by certain medications.

Janumet (metformin and sitagliptin) is used to reduce blood glucose levels in individuals with type 2 diabetes. It works by increasing insulin sensitivity in muscle, fat, and other tissues. Sitagliptin, a component of Janumet, reduces blood sugar levels by inhibiting the DPP-4 enzyme and increasing the levels of the hormones GLP-1 and GIP.


What are the side effects of metformin and Janumet?


The most common side effects of metformin include:

  • Weakness or lack of energy
  • Respiratory tract infections
  • Low levels of vitamin B-12
  • Low blood glucose (hyperglycemia)
  • Constipation
  • Indigestion
  • Muscle pain
  • Heartburn
  • Chills

A serious but rare side effect of metformin is lactic acidosis, which can be fatal. Symptoms of lactic acidosis include weakness, trouble breathing, abnormal heartbeats, unusual muscle pain, stomach discomfort, light-headedness, and feeling cold. Patients with reduced kidney or liver function, congestive heart failure, severe acute illnesses, or dehydration are at greater risk for lactic acidosis.

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The most common side effects of Janumet are similar to those of metformin. Additionally, Janumet should be discontinued immediately if lactic acidosis is suspected.

What is the dosage of metformin and Janumet?


  • For treating type 2 diabetes in adults, the usual starting dose of metformin is 500 mg twice a day or 850 mg once daily. The dose can be gradually increased based on the response of blood glucose levels, up to a maximum daily dose of 2550 mg divided into three doses.
  • If extended release tablets are used, the starting dose is 500 mg or 1000 mg daily with the evening meal. The dose can be increased weekly, up to a maximum dose of 2000 mg, or 2500 mg for Fortamet. Glumetza tablets are given once daily.
  • For pediatric patients 10-16 years of age, the starting dose is 500 mg twice a day, up to a maximum dose of 2000 mg.
  • Children older than 17 years of age may receive 500 mg of extended release tablets daily, up to a maximum dose of 2000 mg.
  • Metformin is safe to use in patients with mild to moderate renal impairment. Renal function should be assessed before starting treatment and regularly thereafter.
  • Metformin should not be used in patients with an estimated glomerular filtration rate (eGFR) below 30 mL/minute/1.73 m2. Starting metformin in patients with an eGFR between 30-45 mL/minute/1.73 m2 is not recommended. Metformin should also be stopped before administering iodinated contrast or in certain patients with liver disease, alcoholism, heart failure, or who will receive intra-arterial iodinated contrast.
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  • Janumet is taken twice daily with meals, and the starting dose is based on the patient’s current dose of sitagliptin and metformin. The maximum daily dose is 100/2000 mg.

What drugs interact with metformin and Janumet?


  • Cimetidine (Tagamet) can increase the amount of metformin in the blood and may increase side effects.
  • Iodinated contrast media can reduce kidney function, leading to increased concentrations of metformin in the blood. Metformin should be stopped before and after the use of contrast media.
  • Thiazide diuretics, steroids, estrogens, and oral contraceptives may increase blood glucose and reduce the effect of metformin. Patients should be observed for signs of low blood glucose when these drugs are stopped.
  • Alcohol consumption increases the risk of lactic acidosis.


  • Cimetidine (Tagamet) can increase the level of metformin in the blood, potentially increasing side effects.

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Are metformin and Janumet safe to use while pregnant or breastfeeding?


  • There are no adequate studies in pregnant women. Most experts agree that insulin is the best treatment for pregnant women with diabetes.
  • Metformin is excreted into breast milk and should not be used by nursing mothers.


  • There are no adequate studies of Janumet or its components in pregnant women. Most experts agree that insulin is the appropriate treatment for diabetes during pregnancy.
  • It is unknown whether sitagliptin is secreted in human breast milk. However, metformin is excreted into breast milk and should not be used by nursing mothers.
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Metformin and Janumet are used to treat type 2 diabetes. Metformin is also used to treat polycystic ovaries and weight gain caused by certain medications used for treating psychoses.


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