That would be a switch from the current scenario, in which companies have an incentive to create "me-too" compounds that don't offer much benefit over a competitor's but sell because they're heavily advertised, argues Jerry Avorn, professor of medicine at Harvard and author of Powerful Medicines: The Benefits, Risks, and Costs of Prescription Drugs. Comparative data would force drug companies "to work harder to discover drugs that are really an improvement over what we have," Avorn says. In the meantime, depressed patients who drift from medication to medication would just welcome a shorter wait.
Correction, April 19, 2006: The original sentence implied that all 20 antidepressants affect serotonin levels. While many of them do, a few drugs work through other mechanisms. Return to the corrected sentence.