TRENTON, N.J. --- A 1999 Merck & Co. study of its since-withdrawn painkiller Vioxx, touted to participating doctors and patients as meant to show whether Vioxx caused fewer stomach problems than another drug, was mainly a stealth marketing strategy, researchers report.

The true purpose was to get doctors and patients in the habit of using Vioxx just in time for its launch, according to doctors who uncovered internal Merck memos discussing the strategy behind the study, called ADVANTAGE. They did so while reviewing roughly a million Merck documents for plaintiffs' lawyers preparing for trials in Vioxx lawsuits.

Drug companies are widely suspected of doing many such "seeding," or marketing studies, but there's been no "smoking gun" proving it before, according to the Annals of Internal Medicine , which published Merck's original report on ADVANTAGE in 2003 and will publish the new report today.

An accompanying editorial, co-written by Annals editor Dr. Harold C. Sox, states that the journal wasn't told the true purpose of ADVANTAGE, which compared Vioxx with an older pain reliever, naproxen, when it published results indicating Vioxx was better tolerated.

Dr. Jonathan Edelman, the head of scientific affairs at Merck Research Laboratories, said Monday "the ADVANTAGE study was primarily a scientific study" designed and executed by the company's clinical research unit and that any later use of data for marketing was a separate operation.

But Dr. Kevin P. Hill said he and colleagues, while working as paid consultants for lawyers representing plaintiffs who claimed Vioxx caused heart attacks or other harm, stumbled on documents indicating Merck's marketing division designed ADVANTAGE and handled the data collection and analysis.

Using funding from the Robert Wood Johnson Foundation's clinical scholars program, they searched further, uncovering items such as a memo from two top Merck executives nominating the study for an internal marketing award.

ADVANTAGE used about 600 family doctors new to clinical research, each getting a stipend plus fees for recruiting patients. Most clinical trials are run by a limited number of specialists at major teaching hospitals that each recruit hundreds of patients.

Vioxx came on the market in June 1999, after rival Pfizer Inc.'s Celebrex. Both makers claimed their drugs caused less cramping, diarrhea and dangerous gastrointestinal bleeding than other pain relievers.

Dr. Hill, now a staff psychiatrist at McLean Hospital in Massachusetts, said he and his colleagues found documents indicating "ADVANTAGE was marketing framed as scientific research."

"I don't think people would be willing to (risk side effects) if they knew that the aim of a clinical trial was to boost profits for a pharmaceutical company," Dr. Hill said.

The study's name implied it had a scientific purpose: ADVANTAGE, or Assessment of Differences between Vioxx and Naproxen to Ascertain Gastrointestinal Tolerability and Effectiveness.

But Dr. Hill said doctors participating in ADVANTAGE got a kit telling them how to talk to other doctors about Vioxx, and that another Merck study, VIGOR, also examined how safe Vioxx was, so ADVANTAGE wasn't needed. VIGOR's results were published in 2000.