World anti-doping officials have doubled the potential punishment for those caught using banned substances for the first time.
Offenders could now face a ban of up to four years if found guilty in "aggravating circumstances".
The move is one element in the revised World Anti-Doping Agency (Wada) code, which is being ratified in Madrid.
"Nobody thinks the code we have adopted is perfect or final," said outgoing Wada president Dick Pound.
"But it's a big improvement on what we had."
The definition of "aggravating circumstances" includes athletes who are found to be:
The new code was approved on the final day of a three-day international conference on fighting performance-enhancing drugs in sports.
"It sends a message to the public that we remain firm in our resolve"
The revised set of rules and sanctions, which also includes reduced punishments for athletes who help authorities catch other drug cheats, will come into effect on 1 January 2009.
Athletes will be considered guilty of a doping violation if they accumulate a combination of three missed tests and/or fail to provide information of their whereabouts within an 18-month period in the new code.
There will also be possible ban reductions for athletes who admit to doping.
And athletes could face lesser sanctions if they can prove the prohibited substance was not intended to enhance performance.
"This is an ongoing process," said Pound. "It sends a message to the public that we remain firm in our resolve."
606: DEBATE
The Wada code, which first went into effect in 2004, is the central set of drug-testing rules across all sports and countries.
"While we can be understandably proud, I think it's also fair to say that the fight against doping is a living exercise," said Pound said.
"It will never cease. There will always be people out there who will break the rules.
"It will continue to require unwavering vigilance and the willingness to tackle those people who are the sociopaths of sport - they'll always be there."
Following complaints from football's governing body Fifa and other team sports, Wada agreed to further discussions on the provision that those serving doping bans should not be allowed to train with their teams.
"I don't want my kid practising every day for a team with someone who's been suspended for drug use," Pound said.
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