when diet and exercise alone have not been enough to control your blood glucose levels. It is used particularly in overweight patients.
Do not take metformin hydrochloride:

If you are allergic to metformin hydrochloride or any of the other ingredients of this medicine
If you have liver problems
If you have severely reduced kidney function
If you have uncontrolled diabetes, with, for example, severe hyperglycemia, nausea, vomiting, diarrhea, rapid weight loss…
If you have severe infection, such as an infection affecting your lung or bronchial system or your kidney
If you are treated for acute heart failure or have recently had a heart attack, have severe problems with your circulation or have breathing difficulties
If you drink a lot of alcohol
Warnings and precautions:

Risk of lactic acidosis:

Metformin hydrochloride may cause a very rare but very serious side effect called lactic acidosis, particularly if your kidneys are not working properly, if you have uncontrolled diabetes, serious infections, liver problems, dehydration.
Stop taking metformin hydrochloride and contact a doctor or the nearest hospital immediately if you experience some of the symptoms of lactic acidosis, as this condition may lead to coma.
Symptoms of lactic acidosis:

Vomiting
Stomach ache
Muscle cramps
A general feeling of not being well with severe tiredness
Difficulty in breathing
Reduced body temperature and heartbeat
Risk of hypoglycemia:

If you take metformin hydrochloride together with other medicines to treat diabetes, that can cause hypoglycemia.
If you experience symptoms of hypoglycemia such as weakness, dizziness, increased sweating, fast heart beating, vision disorders or difficulty in concentration, it usually helps to eat or drink something containing sugar.
Possible side effects of metformin hydrochloride:

All medicines can have side effects. Sometimes they are serious, most of the time they are not.
You may need medical treatment if you get some of the side effects.
Tell your doctor if you notice any of the following and they worry you:
Lactic acidosis which can lead to coma
Digestive problems such as nausea, vomiting, diarrhea, abdominal pain and loss of appetite
Change in taste
Other medicines and metformin hydrochloride:

Tell your doctor if you are using, have recently used or might use any other medicines.
Medicines which increase urine production (diuretics)
Medicines used to treat pain and inflammation (NSAIDs)
Certain medicines for the treatment of high blood pressure
Beta-2 agonists such as salbutamol (to treat asthma)
Corticosteroids
Other medicines used to treat diabetes
How to take metformin hydrochloride:

Recommended dose is:

Children 10 years and over and adolescents:

usually start with 500 mg or 850 mg metformin hydrochloride once a day.
The maximum daily dose 2000 mg taken 2 or 3 divided doses
Adults:

usually start with 500 mg or 850 mg metformin hydrochloride 2 or 3 times a day.
The maximum daily dose is 3000 mg taken as 3 divided doses
How to store metformin hydrochloride:

Keep it out of the reach of children
Do not use this medicine after the expiry date
Store in the original pack in order to protect from light