Diarrhea, gas, upset stomach, constipation, or stomach pain may occur in the first few weeks of treatment as your body adjusts to this medication but usually improve with time. Follow your prescribed diet to help lessen these side effects. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.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.Tell your doctor immediately if any of these rare but very serious side effects occur: unusual tiredness, persistent nausea/vomiting, severe stomach/abdominal pain, rectal bleeding, yellowing eyes/skin, dark urine.Acarbose does not cause low blood sugar (hypoglycemia). However, this effect can occur if you also take other anti-diabetic drugs (e.g., sulfonylureas, insulin) and if you do not consume enough calories from food or if you do unusually heavy exercise. Symptoms of low blood sugar include cold sweat, blurred vision, dizziness, drowsiness, shaking, fast heartbeat, headache, fainting, tingling of the hands/feet, and hunger. Do not use table sugar (also called cane sugar or sucrose) to relieve these symptoms because acarbose delays its breakdown. Carry glucose tablets or gel with you to treat low blood sugar. If you are in a situation where you don't have these reliable forms of glucose, eat some honey or drink a glass of orange juice (sources of another sugar, fructose) to quickly raise your blood sugar level. Tell your doctor about the reaction immediately. 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 dosage may need to be increased or you may need other drugs.A very serious allergic reaction to this drug is rare. However, seek immediate medical attention 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.