The number of children and teenagers taking antidepressants has fallen more than 20 percent this year after U.S. warnings the medicines may increase suicidal tendencies among youth, pharmacy benefits manager Medco Health Solutions Inc. said on Tuesday.

Medco, which acts as an intermediary between employers, health plans and drugmakers, said its research indicates an 18-percent decrease in the number of patients under age 18 who took an antidepressant in the first quarter of 2004.

An additional 5-percent decrease was seen in the second quarter, it said.

The data suggest a turnaround from prescription trends between 2000 and 2003, when there was a combined 25 percent increase in sales of such drugs to children, Medco said.

However, Medco’s findings conflict with estimates of an FDA official, who last week said antidepressant prescriptions for children rose this year despite widespread publicity about risks of the drugs to youth.

The FDA official said his conclusion was based on pharmacy sales figures collected by IMS Health, a consulting company that tracks drug sales.

Medco, which authorizes filling of prescriptions for 60 million Americans in insurance plans, came up with the findings after analyzing prescription patterns among its clients.

Medco said the drop in youth usage began after the U.S. Food and Drug Administration issued an advisory in October 2003 that cited reports of suicidal thoughts and suicide attempts among children treated with certain antidepressants.

Critics charge the agency was slow to act and instead chose to discount the findings of one of its own researchers.

“Studies show that greater caution is needed when treating pediatric and teen depression with medication, and it’s clear that physicians are heeding these warnings,” said Dr. Robert Epstein, Medco’s chief medical officer.

More attention to the risks came in March, when the FDA required makers of 10 antidepressants to include stronger warnings on their package inserts of potential suicidal tendencies among young users.

The risks were further highlighted last week when an advisory panel to the FDA urged the agency to require a “black box” warning of the dangers on the drug labels, the strongest type used for prescription drugs, to get the message to doctors.

The panel said safety concerns applied to nine drugs it has studied. They include Eli Lilly and Co’s. Prozac, GlaxoSmithKline Plc’s Paxil and Wellbutrin, Pfizer Inc.‘s Zoloft, Wyeth’s Effexor and Forest Laboratories Inc.‘s Celexa.

Many of the drugs belong to a class of drugs called selective serotonin reuptake inhibitors, which maximize the presence in the brain of a messenger chemical called serotonin.

The black box warnings should also appear on older antidepressants, including a family of drugs called tricyclics, the panel said.

Moreover, some panelists said the drug labels should reflect that none of the medicines, with the exception of Prozac, have proven effective in children and been cleared by the FDA for pediatric use.