The strategy for the International Equestrian Federation's "Clean Sport" campaign, the result of two commissions of inquiry, was passed by the ruling body's general assembly by a vote of 90-8.
The addition of bute to the progressive list of substances in horse sport has leading equestrian nations worried.
The progressive list allows phenylbutazone (bute), up to 8 micrograms per millilitre in plasma or serum. This is three times the level permitted in the 1980s before the powerful anti-inflammatory agent was banned.
The progressive list also allows salicyclic acid (similar to aspirin) up to 750mcg/ml in urine and up to 6.5 mcg/ml in plasma or serum. Flunixin, a common anti-inflammatory and painkiller in horses, will be allowed up to 500 mcg/ml in plasma or serum.
The new rules allow for a horse with levels below the prescribed limits to pass a drugs test provided the drugs are not used in combination.
The new list also prescribes acceptable levels for acetycysteine, which is used for some respiratory conditions; dichloroacetate (lactanase), which helps prevent tying up by reducing the buildup of lactic acid in muscle cells; and isoxuprine, a blood vessel dilator often used in the treatment of hoof conditions.
Major horse nations are concerned how sponsors will view the FEI's stance on a set of drugs commonly used in horses. Some question how the industry can sell a "clean sport" image when it tolerates the presence of such key substances.
The progressive list received 53 votes in favour, against 48 for the existing list.
The Daily Telegraph reports that major equestrian federations, including the United States, Sweden, Germany, New Zealand, Australia and Ireland spoke passionately against the move to a progressive list.
"The progressive list now permits in-competition use of a limited number of medications under strictly prescribed limits," the FEI said in a statement after the vote.
The assembly also approved an itemised list of more than 1000 substances not allowed in competitive horses.
Despite the clear concern of major horse nations over the new progressive list, the FEI was afterwards singing the praises of the vote in favour of its new Equine Anti-Doping and Controlled Medication Regulations.
The regulations, it said, would ensure the welfare of the horse and guarantee a fair playing field.
FEI president, Princess Haya, commenting on support for the Clean Sport Campaign, said: "This is a true landmark moment in the history of our sport.
"The overwhelming support of the national federations for the Clean Sport Campaign is proof that we are moving in the right direction thanks to the incredible work done by the Ljungqvist and Stevens Commissions.
"This vote has given us the power to roll out Clean Sport and allow us to restore the public image of our sport as a clean and uncorrupt product."
The campaign was the result of a year-long consultation process. The recommendations of the commissions, led by Professor Arne Ljungqvist, chairman of the International Olympic Committee Medical Commission and vice president of the World Anti Doping Agency, and Lord Stevens, a former Metropolitan Police Commissioner.
"Ultimately, it was down to the equestrian community to make the final decision and they have voted in support of the package as a whole, Ljungqvist said.
"The two commissions have put in an enormous amount of work to come up with these recommendations and it is particularly gratifying that we have received such overwhelming support for the Clean Sport Campaign from the national federations."
Lord Stevens said: "We said yesterday that the FEI needed to adopt these recommendations before it could be given a clean bill of health. They have been approved by a massive majority and now the sport can move forward."