Prior to approval from the Food and Drug Administration (FDA), possible negative side effects of prescription drugs are often determined in only small groups of people over short time periods. Pharmaceutical companies also often publicize a drug before all of its side effects are known. As a result, many new drugs may be approved by the FDA without full knowledge of their side effects, and previously unknown side effects are reported to the administration only after some drugs have already hit the market.
A study in the Journal of the American Medical Association determined the relationship between new prescription drugs and the addition of "black box warnings" (warnings required by the FDA to be placed on drug packaging that indicate potentially severe or life-threatening side effects) or removal from the market. The authors examined all new drugs approved from 1975-1999, and all drugs withdrawn from the market for safety reasons from 1975-2000.
An estimated 20% of prescription drugs released to the public during that time received a black box warning or were removed from the market. Half of changes to drug warning labels occurred within seven years of introduction; half of withdrawals from the market took place within two years of introduction.
The safety of new drugs is uncertain until they have been widely used for many years. Don't be one of the first people to suffer a previously unknown side effect of a drug. If you must take a prescription drug, opt for one that is tried and true -- not the heavily marketed, newer one. Also, consider alternative therapies besides drugs to treat your condition.
Lasser KE, Allen PD, Woolhandler SJ, et al. Timing of new black box warnings and withdrawals for prescription medications. Journal of the American Medical Association 2002:287(17), pp. 2215-2220.