German Olympic dressage rider Isabell Werth has been fined and banned from competition for six months following a positive drug test on her horse Whisper.

An International Equestrian Federation tribunal has ruled that Werth was responsible for the infraction, which occurred at a four-star event late in May at Wiesbaden, in Germany.

Her mount Whisper tested positive for the drug Fluphenazine, which had been given to the horse to relieve symptoms of a condition called Shivering Syndrome.

The banned drug is an anti-psychotic medication having long-acting sedative or behaviour-modifying effects.

Werth had explained in an earlier press release how the horse had been prescribed the drug Modecate - which contains Fluphenazine - for the condition by a veterinarian, Dr Hans-Georg Stihl.

Dr Stihl had explained that a "settling period" of six days would probably be enough for the drug to leave the horse's system. In any event, it was 14 days before the horse competed, but the gelding still returned a positive test.

The tribunal, comprising Erick Elstad, Patrick Boelens and Pierre Ketterer, said Werth admitted the violation, but said she had been relying entirely on the "erroneous advice" of Dr Stihl that she could compete six days after the drug's use.

The tribunal ruled that Werth could not absolve herself of fault under the circumstances.

"The tribunal has repeatedly expressed the view that it is the responsibility of competitors to inform themselves of all substances administered to horses which are destined for participation in international events and to ensure that such horses do not have any prohibited substances in their systems.

"The competitors are also responsible for how their staff care for the horses and administer medical treatment to them, which includes veterinarians."

The tribunal said it was "quite shocking" that Dr Stihl believed the detection time for the drug was six days. The United States Equestrian Federation has published a 90-day detection time since 2006, it said.

The tribunal said Fluphenazine is a serious performing-enhancing substance, and that the risk to horse welfare by using it is significant. It was not licensed for use in horses.

In Werth's favour, it said she quickly accepted responsibility and acknowledged the violation. She offered a full explanation as to how the drug entered the horse's system.

The tribunal imposed a six-month suspension, effective immediately, with her provisional suspension, which has run from June 23, able to be credited against it.

Werth was fined 1500 Swiss francs and ordered to pay another 2000 toward legal costs.