What is inside metformin that makes it smell bad and that makes it taste like metal?

medicalmen; most say it smells more like fish, as far as the ingredents they claim it is a chemical reaction of the meds in it, And if you want to avoid the smell it is said to get the timed release from your doctor which has less of a smell. But to date they really don't know what it is from. Chuck1957 here is a write up about it this is a copy and paste about your question. GOOD LUCK Chuck
Can't You Smell That Smell?

Pharmacists and patients are well aware that metformin may come with a fishy smell when you open the bottle. The smell does not mean the drug is spoiled, it's just due to it's inherent characteristics. Metformin is associated with relatively few side effects, but nausea may be one of them, possibly due to this 'fishy' odor.

According to a report published in the Annals of Internal Medicine, some extended-release forms of metformin have a lower odor, and may be less likely to cause nausea. If you can't tolerate your metformin, let your doctor know. A switch to the extended-release form or a different manufacturer may do the trick.