A few things to know:

•   Two different agencies control advertising for drugs. The FDA regulates advertising for prescription drugs and can mandate warnings (like the ones you see at the end of commercials). But for over-the-counter drugs, a different agency, the Federal Trade Commission, oversees marketing claims. 

•   For prescription drugs, the FDA can require so-called black box warnings when drugs pose a potentially "serious or life-threatening" risk. The agency requires all prescription drugs containing acetaminophen to carry a black box warning that an overdose can result in liver transplant or death. For over-the-counter Tylenol and its generic equivalents, the FDA requires no warning that overdose can be fatal.

•  For example, Tylenol with Codeine No. 3, made by a Johnson & Johnson company, combines acetaminophen with codeine and can only be bought with a prescription. Tylenol 3, as it is commonly known, carries a black box warning that overdose can lead to death. By contrast, Extra-Strength Tylenol, sold over the counter, carries no such warning. So: two pills containing acetaminophen, made by the same corporation, carrying the same brand name, sold in the same country, regulated by the same agency are subject to different safety standards.

• The FDA also requires drug makers to disclose the potential dangers of prescription acetaminophen in television advertising, but the FTC does not require the same for advertising over-the-counter versions of the drug.