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.


Codeine is an analgesic drug used in humans for the treatment of mild to moderate pain. It is found in many readily available medication preparations, including over-the-counter tablets, capsules, powders and syrups. Be aware that many Paracetamol and Ibuprofen based preparations also contain Codeine. Codeine in itself is not considered a significant recreational drug, but its addictive properties are well-known and this is of medical concern.


Dimethyl sulfoxide (DMSO) is a natural substance (liquid and solvent) found naturally in the horse, as well as in nature and in horse feed such as lucerne (alfalfa hay) and oats.

DMSO is known to significantly increase the permeability (enhance the transport) of certain substances through the skin of the horse and it has additionally been implicated to have some anti-inflammatory effects. In the horse it can be used both topically (on the skin) and injectable (it can be administered by infusion).

Within the IFHA and at the NHA the use of this prohibited substance in the horse has historically been monitored against an International Threshold of prosecution of 15 µg/ml in URINE and 1000 ng/ml (equivalent to 1 µg/ml) in PLASMA.  While the specified concentrations have remained unchanged, DMSO is now instead controlled by International Residue Limits (IRL’s) of respectively 15 µg/ml in URINE and 1000 ng/ml in PLASMA. 


The NHA recognises the threat which Class 1, Forbidden Substances pose to the integrity of racing and the welfare of the horse. For this reason sophisticated protein and peptide screening methods have been in place at the NHA for close to 20 years. During the year 2000 the NHA Laboratory established collaboration with some other major racing jurisdictions in conducting the initial research and then developing the basis of approaches and methodologies to screen for commercial Growth Hormones (GH’s), their GH releasing precursors, their messenger growth factors and synthetic analogues of such growth factors. The effective screening of a range of different Erythropoietins (EPO’s) which are commercially available was also devised during that time. The range of peptide and protein forbidden substances and substances of concern to racing has since increased and the research and development of screening and confirmation methods for these has not stood still. The NHA has the expertise, experience, set-up and instrumentation required for the screening of such substances. During the racing year 2020/2021 there was screening of such substances employing internationally approved and adopted methodologies. The specimens screened included those from post-race, pre-race and from out of competition collections (unannounced collection of specimens at stable yards). Similar screening is now again in place during the 2021/2022 season.