Weight Gain
Lethargy >.Lack of Energy
Muscle Aches
Head Aches
Decreased Appetite
References :

References :
http://www.generic-rx.net/glucophage.html

http://www.medicinenet.com/metformin/article.htm

As a nurse I see horrible side effects from diabetes that wasn’t controlled well every day. It effects every part of your body, but I have to say the only side effect I’ve seen from any oral hypoglycemic (the class that metformin is in) is low blood sugar.

Metformin should never be taken on a day that you are not going to be eating. It could drop your blood sugar too low. (If your doctor told you sonething different than me – listen to him. This pill is less likely to be a problem than most)

From Web MD: This medication does not usually cause low blood sugar (hypoglycemia). However, low blood sugar may occur, especially if you take other medications for diabetes, drink large amounts of alcohol, do unusually heavy exercise, or do not consume enough calories from food.

Nausea, stomach upset, diarrhea, or a metallic taste in the mouth may occur at first as your body adjusts to the medication. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. If stomach symptoms return later (after you are on 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 a sign of lactic acidosis.

I have never seen this side effect, but it is listed:Metformin can rarely cause a serious (sometimes fatal) condition called lactic acidosis. Stop taking metformin and seek immediate medical attention if you develop any of the following symptoms of lactic acidosis: unusual tiredness, severe drowsiness, chills, blue/cold skin, muscle pain, fast/difficult breathing, unusually slow/irregular heartbeat.

Lactic acidosis is more likely to occur in patients who have certain medical conditions, including kidney or liver disease, conditions that may cause a low oxygen blood level or poor circulation (e.g., severe congestive heart failure, recent heart attack, recent stroke), heavy alcohol use, a severe loss of body fluids (dehydration), X-ray or scanning procedures that require an injectable iodinated contrast drug, recent surgery, or a serious infection. Tell your doctor immediately if any of these conditions occur or if you notice a big change in your overall health. You may need to stop taking metformin temporarily. The elderly are also at higher risk, especially those older than 80 years who have not had kidney tests. (See also Side Effects and Precautions sections.)

References :
http://www.webmd.com/drugs/mono-7061-METFORMIN+-+ORAL.aspx?drugid=11285&drugname=Metformin+Oral