well some have betaine HCL which mimic stomach acid which are great if you have an acid prob and at night time when your metabolism slows....and then there are the plant enzymes more or less without HCL. They are great to just add to the larger meals and to help replace enzymes that arent present in many processed foods. I use them and i am 21 and they are great....they say you dont need them, but they are a great addition to a bulking phase haha.