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Fortamet Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Fortamet (metformin hydrochloride) is for people with type 2 (non-insulin-dependent) diabetes. Metformin is sometimes used in combination with insulin or other medications, but it is not for treating type 1 diabetes. It is an oral diabetes medicine. This medication is available in generic form. Common side effects include nausea, vomiting, stomach upset, diarrhea, weakness, or a metallic taste in the mouth.

Fortamet should be taken once daily. Dosage is individualized based on effectiveness and tolerance. The maximum recommended daily dose is 2500 mg. Hyperglycemia (high blood sugar) may result if you take Fortamet with drugs that raise blood sugar, such as: isoniazid, diuretics (water pills), steroids, phenothiazines, thyroid medicine, birth control pills and other hormones, seizure medicines, and diet pills, or medicines to treat asthma, colds or allergies. Hypoglycemia (low blood sugar) may result if you take Fortamet with drugs that lower blood sugar, such as: alcohol, non-steroidal anti-inflammatory drugs (NSAIDs), aspirin or other salicylates, sulfa drugs, monoamine oxidase inhibitors (MAOIs), beta-blockers, or probenecid. It may also interact with furosemide, nifedipine, cimetidine or ranitidine, amiloride or triamterene, digoxin, morphine, procainamide, quinidine, trimethoprim, or vancomycin. During pregnancy, Fortamet should be used only when prescribed. Your doctor may direct you to use insulin instead of this product during your pregnancy. This medication can cause changes in the menstrual cycle (promote ovulation) and increase the risk of becoming pregnant. Consult your doctor about the use of reliable birth control. This medication passes into breast milk in small amounts. Consult your doctor before breast-feeding.

Our Fortamet (metformin hydrochloride) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is Patient Information in Detail?

Easy-to-read and understand detailed drug information and pill images for the patient or caregiver from Cerner Multum.

Fortamet in Detail - Patient Information: Side Effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

This medication may cause lactic acidosis (a build-up of lactic acid in the body, which can be fatal). Lactic acidosis can start slowly and get worse over time. Get emergency medical help if you have even mild symptoms of lactic acidosis, such as:

  • muscle pain or weakness;
  • numb or cold feeling in your arms and legs;
  • trouble breathing;
  • feeling dizzy, light-headed, tired, or very weak;
  • stomach pain, nausea with vomiting; or
  • slow or uneven heart rate.

Call your doctor at once if you have any other serious side effect such as:

  • feeling short of breath, even with mild exertion;
  • swelling or rapid weight gain; or
  • fever, chills, body aches, flu symptoms.

Less serious side effects may include:

  • headache or muscle pain;
  • weakness; or
  • mild nausea, vomiting, diarrhea, gas, stomach pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Fortamet (Metformin Hcl)

What is Patient Information Overview?

A concise overview of the drug for the patient or caregiver from First DataBank.

Fortamet Overview - Patient Information: Side Effects

SIDE EFFECTS: Nausea, vomiting, stomach upset, diarrhea, weakness, or a metallic taste in the mouth may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. If stomach symptoms return later (after taking the same dose for several days or weeks), tell your doctor immediately. Stomach symptoms that occur after the first days of your treatment may be signs of lactic acidosis.

An empty tablet shell may appear in your stool. This effect is harmless because your body has already absorbed the medication.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Metformin does not usually cause low blood sugar (hypoglycemia). Low blood sugar may occur if this drug is prescribed with other anti-diabetic medications. Talk with your doctor or pharmacist about whether the dose of your other diabetic medication(s) needs to be lowered.

Symptoms of low blood sugar include sudden sweating, shaking, fast heartbeat, hunger, blurred vision, dizziness, or tingling hands/feet. It is a good habit to carry glucose tablets or gel to treat low blood sugar. If you don't have these reliable forms of glucose, rapidly raise your blood sugar by eating a quick source of sugar such as table sugar, honey, or candy, or drink fruit juice or non-diet soda. Tell your doctor about the reaction immediately. Low blood sugar is more likely if you drink large amounts of alcohol, do unusually heavy exercise, or do not consume enough calories from food. To help prevent low blood sugar, eat meals on a regular schedule, and do not skip meals. Check with your doctor or pharmacist to find out what you should do if you miss a meal.

Symptoms of high blood sugar (hyperglycemia) include thirst, increased urination, confusion, drowsiness, flushing, rapid breathing, and fruity breath odor. If these symptoms occur, tell your doctor immediately. Your doctor may need to adjust your diabetes medication(s).

Stop taking this medication and tell your doctor right away if this very serious side effect occurs: lactic acidosis (see Warning section).

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any of the following symptoms of a serious allergic reaction: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire patient information overview for Fortamet (Metformin Hcl)

What is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Fortamet FDA Prescribing Information: Side Effects
(Adverse Reactions)


FORTAMET® (metformin hcl) Clinical Studies

In the controlled clinical studies of FORTAMET® (metformin hcl) in patients with type 2 diabetes, a total of 424 patients received FORTAMET® (metformin hcl) therapy (up to 2500 mg/day) and 430 patients received immediate-release metformin. Adverse reactions reported in ≥ 5% of the FORTAMET® (metformin hcl) or immediate-release metformin patients are listed in Table 6. These pooled results show that the most frequently reported adverse reactions in the FORTAMET® (metformin hcl) group were inf ection, diarrhea, and nausea. Similar incidences of these adverse reactions were seen in the immediate-release metformin group.

Table 6: Number and Percentage of Patients With the Most Common (Incidence ≥ 5%)Treatment-Emergent Signs or Symptoms by Body System and Preferred Term Pooled Phase II and III Studies

Immediate-Release Metformin
Body System
  Preferred Term
n (%) n (%)
Body as a Whole
  Accidental Injury 31 (7.3) 24 (5.6)
  Headache 20 (4.7) 22 (5.1)
  Infection 87 (20.5) 90 (20.9)
Digestive System
  Diarrhea 71 (16.7) 51 (11.9)
  Dyspepsia 18 (4.2) 22 (5.1)
  Nausea 36 (8.5) 32 (7.4)
Respiratory System
  Rhinitis 18 (4.2) 24 (5.6)

The most frequent adverse events thought to be related to FORTAMET® (metformin hcl) were diarrhea, nausea, dyspepsia, flatulence, and abdominal pain. The frequency of dyspepsia was 4.2% in the FORTAMET® (metformin hcl) group compared to 5.1% in the immediate-release group, the frequency of flatulence was 3.5% in the FORTAMET® (metformin hcl) group compared to 3.7% in the im mediate-release group, and the frequency of abdominal pain was 3.3% in the FORTAMET® (metformin hcl) group compared to 4.4% in the immediate-release group.

In the controlled studies, 4.7% of patients treated with FORTAMET® (metformin hcl) and 4.9% of patients treated with immediate-release metformin were discontinued due to adverse events.

Immediate-Release Metformin

Immediate-Release Metformin Phase III Clinical Studies

In a U.S. double-blind clinical study of immediate-release metformin in patients with type 2 diabetes, a total of 141 patients received immediate-release metformin therapy (up to 2550 mg per day) and 145 patients received placebo. Adverse reactions reported in greater than 5% of the immediate-release metformin patients, and that were more common in immediate-release metformin- than placebo-treated patients, are listed in Table 7.

Table 7: Most Common Adverse Reactions (>5.0%) in a Placebo-Controlled Clinical Study of Immediate-Release Metformin Monotherapy*

  Immediate-Release Metformin Monotherapy
(n = 141)
(n = 145)
Adverse Reaction % of Patients
Diarrhea 53.2 11.7
Nausea/Vomiting 25.5 8.3
Flatulence 12.1 5.5
Asthenia 9.2 5.5
Indigestion 7.1 4.1
Abdominal Discomfort 6.4 4.8
Headache 5.7 4.8
* Reactions that were more common in immediate-release metformin than placebo-treated patients

Diarrhea led to discontinuation of study medication in 6% of patients treated with immediate-release metformin. Additionally, the following adverse reactions were reported in ≥ 1.0 - ≤ 5.0% of immediate-release metformin patients and were more commonly reported with immediate-release metformin than placebo: abnormal stools, hypoglycemia, myalgia, lightheaded, dyspnea, nail disorder, rash, sweating increased, taste disorder, chest discomfort, chills, flu syndrome, flushing, palpitation.

Pediatric Patients

No pediatric clinical studies have been conducted with FORTAMET® (metformin hcl) . In clinical trials with immediate-release metformin in pediatric patients with type 2 diabetes, the profile of adverse reactions was similar to that observed in adults

Read the entire FDA prescribing information for Fortamet (Metformin Hcl)

Fortamet - User Reviews

Fortamet User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Fortamet sorted by most helpful. Patient Discussions FAQs

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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