Newborn formula is basically pure lactose, not to mention the taste which is often unpleasant to adults. But there is formula for older kids (1+ years, 2+ years) which doesn't taste bad and is closer to what adults can also drink. Maybe something like that would be suitable for you?
I just checked the iron thing: Apparently adults between 20 and 50 years need more iron in a day than infants do, so I doubt that formula contains toxic amounts. I've never had any negative reaction to the formula I use, though I don't drink that on the daily...
Anyway, there might be more than needed of certain ingredients in formula, but usually, your system will just get rid of what it can't use. I'm not a dietary expert, mind you, but that is what we were taught in biology class^^
Edit: Oops, looks like I was a bit too slow.