I take 3 tylenols at a time, too. The pediatric doxe of tylenol scales up from birth to about 100 lbs and is a straight 15mg of tylenol per kg of body weight. Well, I weigh 225lb, which is just a hair over 100kg, so if I scale up from the kids dose I should take 1500mg of tylenol -- which is 3 extra-strength tylenol. I have this constant battle with my husband, because the bottle says that you should only take 2 at a time. Sure, 2 at a time is the right amount if you weigh 150lb, and even a bit of an overdose if you weigh 110lb, but at my weight I need more than that! I use as my proof what happens if I get a fever. If I take 2 tylenol the fever will break about a half-hour later, and then it will come back 2-1/2 hours after that and then I'll have to wait another miserable hour for another dose. If I take 3, then the fever stays gone for about 4.5 to 5 hours.
The other question about the tylenol 3's -- I assume you mean the combination of tylenol and codeine. They actually have mapped the gene that determines this, and approx 30% of the population does not react to codeine at all. I've always had to be very careful about constipation, and talk about NO effect -- heck codeine doesn't even make ME constipated LOL! Think of us as like cats: did you know that 20% of cats are uneffected by catnip? I haven't had any definitive test showing codeine insensitivity, but I'm pretty suspicious because tylenol 3 always acts on me according to the amount of tylenol in it. If you look at the package insert it should tell you how many mg of each thing is in each pill and then you can do the arithmetic -- and if codeine doesn't have any effect on you then off course you should stick to just plain tylenol. It's a heck of a lot safer, not to mention it's a lot cheaper!
-- cathy :-)