Side effects associated with biguanides often can be greatly reduced by taking the medication with food. Potential side effects include:

• Vomiting
• Diarrhea
• Breathing difficulties
• Nausea or other stomach symptoms
• Abdominal bloating or gas
• Buildup of lactic acid in the blood (lactic acidosis)
• Resumption of ovulation in premenopausal women who had stopped ovulating

Some patients may find that use of biguanides impedes the body’s absorption of vitamin B12. This can increase the risk of B12 deficiency, which causes nerve damage and other problems. It is especially important to avoid this because people with diabetes are already at risk of nerve damage from diabetic neuropathy. A physician may suggest vitamin supplements as a way to restore proper levels of vitamin B12.

Biguanides can cause a significant increase in ovulation (up to eight times). As a result, biguanides are sometimes used to treat polycystic ovarian syndrome. Women taking biguanides should consult with a physician about the medication’s affect on fertility.   

Patients taking the combination medication metformin and glyburide may experience the following side effects:

• Skin reaction
• Dark urine
• Increased sensitivity to the sun

Symptoms of overdose can be similar to the medication’s side effects but are usually more severe.

Biguanides usually interact well with most other medications. However, patients should consult their physicians before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications.

Patients who take biguanides must be careful to limit their consumption of alcohol, as they can become sick if they consume more than two to four drinks a week.

Medications that may interact poorly with biguanides include:

• Calcium channel blockers, a group of antihypertensives
  
  
• The antibiotics trimethoprim (Proloprim) or vancomycin (Vancocin)
  
  
• The diuretics amiloride (Midamor), furosemide (Lasix) or triamterene (Dyrenium)
  
  
• The gastrointestinal medications cimetidine (Tagamet) or ranitidine (Tritec, Zantac)
  
  
• The heart medications digoxin (Digitek, Lanoxicaps, Lanoxin), procainamide (Procanbid) or quinidine (Cardioquin, Quinaglute, Quinidex, Quinora)
  
  
• Morphine, an opioid painkiller
  
  
• Quinine (Quinamm, Quiphile), used to treat malaria
  
  
• Warfarin (Coumadin), an anticoagulant