We tried just about everything on the market when I lost my milk.
Some were TERRIBLE for us (especially the ones with so-called "gentle proteins". :P They not only made my son various degrees of gassy/ill...the decomposed FAST. I mean, I opened his bottle 15-30 minutes after pouring it and WHEW! What a STINK. No flipping wonder they made him sick. The one with broken hearts on the label was the worst...no kidding...truth in advertising: this formula will break your heart! ;), some were okay, some were great. Our favorite, and what we eventually stuck with was Enfamil Lipil.
Except for the ones that caused violent reactions (that we did a rapid switch OFF of) we took a day or two to phase them in, a week or so of use, and a day or two to phase out/in to the next.
The thing is: Everyone reacts to chemicals differently. I'm talking about the chemicals that are found in foods and medicines (fructose, galactose, all the other -ose's; protiens of various sources/compositions/completeness; lipids, vitamins and minerals & the sources THEY come from; H20...just to list the major building blocks). While Enfamil worked wonderfully for OUR son, it could be awful for someone elses. The trick is to learn your baby's system. Watch for changes & reactions, positive or negative.
So too, if you're using tapwater try switching to bottled if your water is fluoridated. Fluoride should never be taken internally (because it's carcinogenic, more so in fact then cigarettes, when tested in labs), but my Aunt is on the H20 board...and it'll probably never be taken out. Public Health wants it too much, since it has cut down so much on low-income pediatric dental work, the politics will never let it. In any event...fluoride also makes a percentage of the population nauseous, and a percentage of that percentage quite ill (gas, constipation, diarrhea, cramps, headache, etc.)
Oops...I do go on.
Good Luck!
Oh! BTW, I just read in another response about the Melamine and looked it up. Looks like the FDA says "No Contamination".
One less thing. Huzzah.
http://www.enfamil.com/app/iwp/MJN/Content2.do?dm=enf&...