I am not a Dr. so these comments are just those of someone who has self educated on the disease we have.

Metformin peaks in the system a few hours after taking it approx 2 hours (plus or minus). It has a half-life of 6-18 hours. It is not metabolized, but passed in the urine. In other words it reduces by 75% after at least 36 hours and after 2 days you have about 10% of it left in your body.

What concerned me about your question is the implication that you have stopped taking the metformin without consulting your Dr. though I may be wrong.

Metformin is from the biguanide group of drugs. These drugs are usually prescribed to help those with insulin resistance make better use of the insulin their pancreas produces or they are having to inject as their pancreas does not generate enough insulin, which I assume is the case with yourself.

Your weight loss will have helped reduce your insulin resistance and as I assume you have reduced your food intake to lose the weight, the insulin you are taking may be able to cope without the metformin. Given the side effects of the condition we have, I would check with your Dr that it was OK to stop taking it, if you have not done so already.

To answer your original question, the research I did when coming off Metformin indicated that it takes 3-4 weeks for Metformin to leave your system - about the same as takes to reach peak effectiveness.

In comparing Metformin and insulin, neither is "evil" Both are the oldest, best tested drugs for diabetic treatment.

The benefits of supplementary insulin are pretty self-explanatory. If your beta cells can non longer produce enough insulin, you need to supplement. Basal (long-acting, background) insulin, such as Lantus, is the first choice when beginning insulin therapy. The biggest risk is the chance of hypoglycemia with too high a dosage. Using a bolus (fast-acting) insulin such as Levemir increases the risk of hypo's just due to inherent inaccuracy in calculating a dosage to cover a meal. Insulin-stimulating drugs also increase the risk of hypoglycemia, are more difficult to customize for individual meals and have not been tested for as long as injectable insulin.


Metformin works primarily by quieting the liver, which is responsible for responding to lows by releasing sugar into the bloodstream. With diabetes, the liver often responds too soon, ie when the person is in a normal range, or the liver releases too much sugar, causing that normal number to go pretty high. So met muffles that response a bit. While it theoretically never causes a low, it does help with fasting numbers that can get out of whack due to dawn phenomenon, and it can limit highs after exercise.

Met has a secondary effect of lowering insulin resistance so that insulin is used more effectively. Metformin has no effect on insulin production capability - for that you need insulin or an oral medication that stimulates insulin production from your pancreas.

Met also has some unrelated effects--it lowers triglycerides and heart risk, may aid with weight loss in the first year of use and there is currently some research into it being a deterrent to some cancers and Alzheimers.

IMO, the most important thing is bringing glucose levels down into "normal" range. Hopefully, your recent bloodwork will show whether or not stopping medications is an option for you.