Metformin has a tissue specific effect on AMPK and reduced food intake and weight loss come from its action through neuronal and endocrine mechanism. See the attached review for further info.

Hope it is useful

Nagaraj 

Metformin for Weight Loss

In regard to weight loss, Metformin provides two primary benefits. First, it significantly improves glycemic control. This stabilizes your blood sugar, and makes you less likely to experience the up-and-down rollercoaster experience that often comes along with dieting. The second benefit of Metformin (partially a result of the first benefit) is suppressed appetite.

Users typically note a measurable improvement from their usual cravings for food. By simply not desiring as much food, and still feeling normal despite eating less (due to the improved glycemic control), the result can be profound weight loss.

That’s the good news, but you can’t just take the pill and expect everything to change on its own. Weight loss just doesn’t work that way. Metformin won’t work for you – rather, it will work with you.

http://www.zenfatloss.com/metformin-weight-loss/

Glucophage has been been linked to a lot of serious side effects. Lowering Blood sugar when it's not high could also make it too low, and therefore dangerous. Why not just try light diets and exercising.

Thank you Ali for the interesting answer

Thanks to everyone for your answers.

Dear Prof. Krishnan, you are correct to specify that diet and exercise does play important role in controlling diabetes, but not for those who are severely diabetic. There is no precise diet that could actually "cure" a diabetic patient, so medications are essential or additive (they do not cure diabetes either). As for metformin, this particular drug (a biguanide) is one of the safest among most of the anti-diabetic medications, since metformin do not cause hypoglycaemia even in fasting state (this is one advantage). So, the risk of low blood sugar leading to hypoglycaemia is minimal. One important adverse effect of this drug is lactic acidosis, but which occurs rarely - and when the drug is taken with alcohol. Otherwise, metformin is relatively safe when compared to Sulfonylurea class of drugs. As Prof. Ali noted above, metformin is good for those who are obese and overweight, since there is evidence of metformin-induced weight loss in type II diabetic patients.

Best Regards, Sidharta

There has been some ongoing research about the safety and efficacy of metformin in preventing diabetes in obese.

As regard to toxicity of metformin, it is relatively safe since it is excreted unchanged in the urine, not at all metabolized, so do not generate toxic metabolites.

One study points out that:

"As previously reported by Medscape Medical News, metformin therapy may represent a more cost-effective alternative to lifestyle changes for preventing diabetes."

http://www.medscape.com/viewarticle/760740

Metformin manages to control the amount of sugar in the blood in three distinct ways. Firstly it works on the food that you eat. Most foods have some degree of sugar in them and too much can cause the diabetes to become worse. The amount that the body absorbs is important and Metformin makes sure that not too much gets through. If too much does get through the body cannot deal with it and it is then that you become ill. Secondly it keeps down the amount of sugar that is produced by the liver. If this can be slowed down, there will be less sugar travelling around the body and the outcome will be that you are less likely to be ill. Its final function is to make sure that insulin is regulated. It works on both injected insulin and that produced naturally by the body. As a result of this some people who already have to inject may find that they no longer have to do this, or at least cut down the amount of times they have to do it.

http://www.healthguidance.org/entry/15193/1/Metformin--What-Every-Diabetic-Should-Know.html

It's extremely tasty to eat oatmeal with a lemon or an orange,honey and nuts to change sugar to natural elements.Fruits,honey,natural juice and wine.

One of Metformin's mechanisms is to restore insulin receptor sensitivity.  Insulin resistance is a characteristic of both type I and II diabetes, resulting in hyperinsulinemia in type II diabetics.  Insulin drives glucose into cells, where it is stored as fat. That is why most type II diabetics are overfat.  By restoring insulin sensitivity, insulin levels are normalized, resulting in less gain of bodyfat.  Metformin also causes increased release of growth hormone, which results in increased lean body mass.  Consequently, a not-infrequent seemingly paradoxical result of Metformin use is a GAIN in bodyweight, and a simultaneous reduction in waist circumference and clothing size, due to this morphogenic shift of less body fat and increased lean body mass. 

There is a drag called "Competact 15mg/850mg" which contain metformin and pioglitazone". I observe that this drag after 3-4 hours can  result in hypoglycemia. One needs to eat something at this time. It seems that it is more effective that metformin alone.

metformin (glucophage) causes weight loss because it is used to control excess sugar (glucose) in the blood. It reduces the quantity of circulating sugar and any substance that can do that will cause weight loss. It controls excess sugar by sending it to the kidney for excretion instead of converting the excess sugar to glycogen that can enhance weight gain

Thanks Angela for your answer.

Metformin, to some great extent, supress hepatic gluconeogenesis besides inhibiting glucagon-induced increase in cAMP levels. Regarding suppression of hepatic gluconeogenesis, metformin indirectly inhibits the gluconeogenic enzymes (via activation of AMPK).

It is of no doubt that metformin reduces circulating free sugar (by stimulating peripheral glucose uptake) but I am sceptic about the mechanism you have pointed out:

" It controls excess sugar by sending it to the kidney for excretion instead of converting the excess sugar to glycogen that can enhance weight gain"

Is  there any research pointing out to this theory?

Regards, Sidharta

Dear Sidharta, The effect of AMPK activation on energy metabolism is dependent on whether AMPK is activated in the hypothalamus or peripheral tissues.In general, AMPK activation in the hypothalamus increases food intake and decreases energy expenditure and increases while peripheral AMPK activation increases energy expenditure (see our recent review Van Dam et al. Regulation of brown fat by AMPK. Trends Mol Med 2015). We observed that activation of brown fat contributes to the weight loss induced by metformin (Geerling et al. Metformin lowers plasma triglycerides by promoting VLDL-triglyceride clearance by brown adipose tissue in mice. Diabetes 2014). Hope this is helpful! Best, Patrick

Look to the permeability of metformin across the CNS blood-barrier. As Dr. Rensen pointed out, effects of AMPK on energy expenditure and food intake are observed after activation of AMPK in the CNS (hypothalamus)

Although i rodent models metformin is associated with weight loss no consistent weight loss effect has been noticed in human stidies-in fact in a review on obeze infertile males there were no conclusive evidence tha just by themselvs metformin is useful for getting fertility restored in obese males and yes the effect on hypothalamus and liver counts and what dosage it is tolerated -in fact it is much more convenient to use glp1 agonists like liraglutide in such patients which not only helps to reduce hba1c levels but is associated with remarkable weight loss irrespective of diabetic status or not in the obese psrson .

I agree that use of GLP-1 receptor agonists make more sense.