The FEI has warned riders to be on the alert for Synephrine contamination, following an unprecedented number of positive tests to this banned substance in show jumping horses this spring. So far 10 horses have tested positive to it at FEI shows – eight of them in Mexico and two in Spain.

The FEI said: “Although investigations into the sources of the positive cases are still ongoing, the FEI would like to warn stakeholders of synephrine which may be found in the horse’s environment and advise on measures that can be taken to prevent a positive finding.”

Synephrine is a stimulant which can cause vasoconstriction, an increased heart rate and is used as a weight loss aid.

It is naturally occurring in some countries common rush (Juncus usitatus), Mullumbimby couch (Cyperus brevifolus) and the leaves of citrus trees (eg. mandarin, orange and lemon) and has also been detected in Teff grass hay and in citrus food flavourings.

Riders are recommended to use reputable feed suppliers, to check the horse’s environment for relevant plants, and to ensure all those caring for horses wash their hands thoroughly after coming into contact with the substance.

Synephrine is a “specified substance” that is “more likely to have been ingested by horses for a purpose other than the enhancement of sport performance, ” but the FEi warns it does not mean it should be considered less dangerous.

The full FEI notice can be read here.