remaaaa,

As per Dr. Furhman, one should not fast while on any medication.

You may try juicing with green vegetables instead of fasting. Also find other ways to get off the medication slowly then you may fast to heal thoroughly.

Scraping your tongue helps with foul smell, but that is part of fasting. No toothpaste.

Archus

Metformin increases your insulin sensitivity, which fasting increase on its own. I can't tell, though, if you can stop it cold turkey - rather not. There is a fasting clinic in Bulgaria where diabetics type 2 fast without medication (on fruits! and herbal tea-honey!) - imagine how the insulin sensitivity increases. You need to make some research:
http://en.emilova.eu/
Please share!
p.s.
There is link btw PCO and decreased insulin sensitivity (=insulin resistance). This is why you were prescribed with it.
Metformin is less effective than lifestyle modifications. Don't consume fats together with carbs. Bring your blood lipids to normal concentrations and ratio. Achievable by green juicing alone, as arcus pointed out.