The former Festina team leader told the court in Lille, northern France: "I took doping substances. I didn't have the choice.
"I was the sheep - if they threw me out of the herd I was finished," he continued.
The admission was a sharp about-turn for the 30-year-old, after he insisted on the trial's opening day that he had never knowingly taken drugs.
"I live in a world where the rules are set up a long time in advance. I didn't cheat other riders.
"In the pack you never use the word doping but medical help. You are doped only when you get caught," he added.
Virenque's lawyer Eric Hemmerdinger, in an apparent change of strategy, then requested that his client be allowed to give further evidence at the opening of Tuesday's session.
Former teammate Luc Leblanc, called as a witness, also told the court he was guilty of drug-taking but he said this had played no part in his winning the 1994 world road race title in Agrigente, Italy.
Since the drug-taking scandal that rocked the 1998 Tour de France, Virenque had always maintained that he never used banned products.
The Frenchman is charged with helping and inciting the administration of illegal substances to other riders.
He is the only rider on trial and could be sentenced to up to two years in jail and fined up to 100,000FF (about £10,000) if found guilty.
The trial, which follows nearly two years of accusations and counter-accusations in France over drug-taking among professional cyclists, is expected to last at least another two weeks.