Arsenic is a so-called heavy metal which can be highly harmful to the horse when administered in significant amounts. When ingested orally it has been shown to cause serious and life-threatening toxic effects in the gastrointestinal tract. As a result of this toxicity, and in an attempt to protect its cells and tissues from dangerous metal poisoning, administered amounts are rapidly excreted by the horse.

It is known that some supplements and tonics contain Arsenic and there are unsubstantiated claims of beneficial effects from its use.  The NHA and the International Federation of Horseracing Authorities (IFHA) are deeply concerned that the use of such preparations could be detrimental or life-threatening to the horse. For this purpose, and in the interest of horse welfare, there are international prosecution thresholds in place for total Arsenic in racehorse urine as well as in blood (plasma). These are indicated on the websites of the NHA and the IFHA.

Please note that Arsenic is present in the natural environment in soil, water and air. It is therefore also found naturally in the horse at a low concentration. It is found more prominently in soil originating from deep mining of gold and other mining processes. Please note that these international thresholds will not be exceeded when local racehorses are exposed to such environments of soil, water and air.

The use of arsenic containing supplements and tonics in the horse have however shown that this threshold is readily exceeded to a significant degree, with total Arsenic concentrations sometimes indicating alarmingly high levels. The IFHA and NHA recommendation is not to use any Arsenic containing preparations in a racehorse a full 2 calendar days prior to the day of the race.