Metformin vs. Insulin, What is the Difference?

Metformin vs. Insulin, What is the Difference?

Diabetes is managed with the use of metformin and insulin. One distinction is that insulin can be used to treat both type 1 and type 2 diabetes, whereas metformin is exclusively used to treat type 2 diabetes. Metformin is also used to treat weight gain brought on by drugs used to treat psychoses, as well as polycystic ovaries. Insulin is supplied intravenously, while metformin is taken orally (subcutaneously). Metformin is sold under the brand names Glumetza, Glucophage, and Fortamet. Similar side effects of insulin and metformin include nausea. Vomiting, gas, bloating, diarrhea, and loss of appetite are metformin side effects that are distinct from those of insulin. Low blood sugar is one of the different side effects of insulin from metformin (hypoglycemia). Confusion, thirst, fatigue, perspiration, headache, heart palpitations, numbness around the lips, tingling in the fingers, tremors, muscle weakness, impaired vision, a cold feeling, yawning, impatience, and loss of consciousness are all signs of hypoglycemia.

What is Metformin? What is Insulin?

Metformin is an oral medicine used to treat type 2 diabetes that decreases blood glucose (sugar) through affecting the body's sensitivity to insulin. The blood sugar levels are reduced by metformin because it makes the liver, muscle, fat, and other tissues more responsive to the effects of insulin. When used alone, metformin does not raise the blood's concentration of insulin or result in hypoglycemia, or low blood sugar. Diabetes consequences like heart disease, blindness, and renal disease can all be decreased with metformin. Metformin is also used to treat weight gain brought on by drugs used to treat psychoses, as well as polycystic ovaries.

The body's cells need insulin, a naturally occurring hormone released by the pancreas, to absorb and use glucose from the blood. Diabetes mellitus patients have a decreased capacity to absorb and utilize glucose from the blood, and their blood glucose levels rise. The pancreas cannot create enough insulin when a person has type 1 diabetes. Patients with type 2 diabetes create insulin, but the insulin is not properly absorbed by the body's cells. Insulin helps to prevent or lessen the long-term effects of diabetes, such as harm to the blood vessels, eyes, kidneys, and nerves, by increasing the uptake of glucose by cells and lowering the blood glucose content. A skin injection is used to give insulin (subcutaneously).

What are the side effects of metformin and insulin?


The most common side effects with metformin are nausea, vomiting, gas, bloating, diarrhea and loss of appetite. These symptoms occur in one out of every three patients. These side effects may be severe enough to cause therapy to be discontinued in one out of every 20 patients. These side effects are related to the dose of the medication and may decrease if the dose is reduced.

Metformin may also cause weakness or lack of energy, respiratory tract infections, low levels of vitamin B-12, low blood glucose (hypoglycemia), constipation, indigestion, muscle pain, heartburn, and chills.

A serious but rare side effect of metformin is lactic acidosis. Lactic acidosis occurs in one out of every 30,000 patients and is fatal in 50% of cases. The symptoms of lactic acidosis are weakness, trouble breathing, abnormal heartbeats, unusual muscle pain, stomach discomfort, light-headedness, and feeling cold. Patients at risk for lactic acidosis include those with reduced function of the kidneys or liver, congestive heart failure, severe acute illnesses, and dehydration.

Hypoglycemia is the most common side effect that may occur during insulin therapy. Symptoms of hypoglycemia include:

Heart palpitations
Numbness around the mouth
Tingling in the fingers
Muscle weakness
Blurred vision
Cold temperature
Excessive yawning
Loss of consciousness

Patients who have excessive blood sugar levels for a long time and then have the elevated levels quickly returned to normal may develop blurred vision. This is brought on by a fluid change in the eye's lens. Vision gradually gets back to normal. Headaches, skin responses (redness, swelling, itching, or rash at the injection site), worsening of diabetic retinopathy, changes in how body fat is distributed (lipodystrophy), allergic reactions, salt retention, and overall body edema are additional adverse effects that may happen. Insulin increases body weight and may lower potassium levels in the blood. Insulin was breathed in addition to these negative effects. (Afrezza) may cause coughing, throat discomfort, or pain; patients should report any persistent lung-related symptoms to their healthcare provider for further evaluation.

What drugs interact with metformin and insulin?


  • Cimetidine (Tagamet), by decreasing the elimination of metformin from the body, can increase the amount of metformin in the blood by 40%. This may increase the frequency of side effects from metformin.
  • Ioversol (Optiray) and other iodinated contrast media may reduce kidney function, which reduces elimination of metformin, leading to increased concentrations of metformin in the blood. Metformin should be stopped 48 hours before and after use of contrast media.
  • Thiazide diuretics, steroids, estrogens, and oral contraceptives may increase blood glucose and reduce the effect of metformin. When these drugs are stopped, patients should be closely observed for signs of low blood glucose.
  • Alcohol consumption increases the effect of metformin on lactate production, increasing the risk of lactic acidosis.


A number of substances affect glucose metabolism and may require insulin dose adjustment and particularly close monitoring.

The following are examples of substances that may reduce the blood glucose-lowering effect of insulin that may result in hyperglycemia:

  • corticosteroids,
  • danazol,
  • diazoxide,
  • diuretics,
  • sympathomimetic agents (e.g., epinephrine, albuterol, terbutaline),
  • glucagon,
  • isoniazid,
  • phenothiazine derivatives,
  • somatropin,
  • thyroid hormones,
  • estrogens,
  • progestogens (e.g., in oral contraceptives),
  • protease inhibitors, and
  • atypical antipsychotic medications (e.g., olanzapine and clozapine).

Oral diabetes medications, ACE inhibitors, disopyramide, fibrates, fluoxetine, MAO inhibitors, pentoxifylline, propoxyphene, salicylates, and sulfonamide antibiotics are a few examples of medicines that may increase the blood glucose-lowering action of insulin and susceptibility to hypoglycemia. Alcohol, beta-blockers, clonidine, lithium salts, and other drugs may either enhance or lessen the ability of insulin to drop blood sugar. Hypoglycemia from pentamidine may occasionally be followed by hyperglycemia. Additionally, the signs and symptoms of hypoglycemia may be diminished or nonexistent when sympatholytic medications such beta-blockers, clonidine, guanethidine, and reserpine are taken. The absorption of inhaled human insulin may be affected by bronchodilators and other inhaled substances.