Should you take metformin if you are prediabetic ?

This is a great question for your doctor.

If you are already using metformin - and now you have an A1C of 6.5 or lower - it is very likely BECAUSE of the metformin and the medication should probably be continued.  Stopping medication could cause this A1C to go up again.

If you are not already using metformin - then discuss options with your doctor and make sure you understand WHY your doctor thinks you would benefit from using metformin instead of just trying to control your prediabetes with diet and exercise.

You should never take anything your doctor has not prescribed.  

You should also never stop taking something that your doctor has prescribed without discussing it with your doctor.  

You should only take medication as per your doctor's advice. 

definitely not.. hypoglycaemia is a real risk for death, and Metformin can easily cause instant delirium and death especially with normal or low blood glucose/sugar level.. the drug can be taken only if you are known diabetic and under doctor's supervision.. if the doctor tells you to take Metformin; it would mean that you are already diabetic and no longer prediabetic..