Turning to private responses to the in formation asymmetry can persist for an extended period for even homogeneous post-experience goods Turning to private responses to the information asymmetry inherent in the primary markets for post-experience goods, we expect secondary markets in gen eral to be less effective than they are for experience goods because of learning prob lems. Nevertheless, secondary markets can play important roles. For example consider the services that are or have been privately offered to provide informa- tion about pharmaceuticals. The Medical Letter on Drugs and Therapeutics, one of the few medical periodicals that covers its costs through subscriptions rather than ad vertising, provides independent assessments of all new drugs approved by the and some have formulary committees that information about drugs for participating physicians. Between 1929 and 1955, th American Medical Association ran a seal of acceptance program that subjected a products advertised in the Journal of the American Medical Association to committe The National Formulary and the United States Pharmacopoeia were i attempts at standardizing pharmaceutical products. Of course, most of these formation sources are directed at physicians and pharmacists who commonly ser for drugs. learning observation may not be effective, they can often determine if advertising claims products are based on reasonable scientific evidence.