Ernie commented recently on the drug side effects in the commercials, and suggests that maybe this is a strategy to limit liability.
At first blush it seems counter-productive. But, if you consider the inevitable litigation that will ensue, it's actually a very smart move. As we all know by now, people don't pay attention to warnings, so why not feature them prominently in TV ads?
Actually, there's a simple answer for this: they are required to disclose the side effects by the FDA under 21 CFR 202.
An exception is made for "reminder advertisements", which the FDA defines as "those which call attention to the name of the drug product but do not include indications or dosage recommendations for use of the drug product". In other words, if you tell us what a drug does, you have to tell us about the potential side effects. However, if you just tell us to ask our doctor about the little purple pill, you don't have to tell us that it causes bloating, diareaha, or any other such unpleasantries.
That said, the Tequila commercial is hilarious... go to Ernie's site and click the link. ("Alcohol may be a factor in getting your ass kicked!")