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Last reviewed on RxList: 3/7/2017
Riomet Side Effects Center

Last reviewed on RxList 11/16/2015

Riomet (metformin hcl) is an oral diabetes medicine used with a proper diet and exercise program and possibly with other medications to control high blood sugar. Riomet is used in patients with type 2 diabetes (non-insulin-dependent diabetes). Riomet is not for treating type 1 diabetes. Riomet is available in generic form. Common side effects of Riomet include nausea, vomiting, stomach upset or pain, diarrhea, gas, weakness, headache, muscle pain, or a metallic taste in the mouth. Go to an emergency department if you experience serious side effects including numb or cold feeling in your arms and legs, trouble breathing, dizziness, light-headedness, tiredness, extreme weakness, or slow or uneven heart rate.

Dosage of Riomet is individualized on the basis of effectiveness and tolerance. The maximum recommended daily dose is 2550 mg (25.5 mL) in adults and 2000 mg (20 mL) in pediatric patients (10-16 years of age). Hyperglycemia (high blood sugar) may result if Riomet is taken with drugs that raise blood sugar, such as: isoniazid, diuretics (water pills), steroids, phenothiazines, thyroid medicines, birth control pills and other hormones, seizure medicines, diet pills, or medicines to treat asthma, colds or allergies. Hypoglycemia (low blood sugar) may result if Riomet is taken with drugs that lower blood sugar, such as: nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin or other salicylates, sulfa drugs, monoamine oxidase inhibitors (MAOIs), beta-blockers, or probenecid. Riomet may also interact with furosemide, nifedipine, cimetidine, ranitidine, amiloride, triamterene, digoxin, morphine, procainamide, quinidine, trimethoprim, or vancomycin. Tell your doctor all medications and supplements you use. During pregnancy, Riomet should be used only when prescribed. Your doctor may prescribe insulin instead during your pregnancy. Riomet can promote ovulation and increase the risk of becoming pregnant. Consult your doctor about birth control while using this medication. This drug passes into breast milk in small amounts. Consult your doctor before breastfeeding.

Our Riomet (metformin hcl) 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.

Riomet Consumer Information

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 Riomet (Metformin Hcl)

Riomet Professional Information


Clinical Studies Experience

In a U.S. double-blind clinical study of metformin in patients with type 2 diabetes, a total of 141 patients received metformin therapy (up to 2550 mg per day) and 145 patients received placebo. Adverse reactions reported in greater than 5% of the metformin patients, and that were more common in metformin- than placebo-treated patients, are listed in Table 1.

Table 1: Most Common Adverse Reactions ( > 5.0 Percent) in a Placebo-Controlled Clinical Study of Metformin Monotherapy*

Adverse Reaction Metformin Monotherapy
(n = 141)
(n = 145)
% 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 metformin-than placebo-treated patients.

Diarrhea led to discontinuation of study medication in 6% of patients treated with metformin. Additionally, the following adverse reactions were reported in ≥ 1.0 to ≤ 5.0% of metformin patients and were more commonly reported with 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

In clinical trials with 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 Riomet (Metformin Hcl)

Related Resources for Riomet

Read the Riomet User Reviews »

© Riomet Patient Information is supplied by Cerner Multum, Inc. and Riomet Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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