Please note this notice supersedes and replace a similar, previous NHA notice on Bisphosphonates, dated 2019. 

Bisphosphonates is a class of drug which prevents the loss of bone density in the racehorse.
These substances are prohibited substances within the Rules of the NHA:

73.4.1 Substances capable at any time of causing an action or effect, or both an action and effect:

… 73.4.1.6 the musculoskeletal system; 


Clenbuterol hydrochloride is a beta-2 adrenergic agonist bronchodilator drug that acts on receptors in the lungs to relax the muscles of the lower small airways to cause dilation of these airways. 

Ventipulmin® is the only registered product for the treatment of inflammatory airway disease (IAD) (also known as equine asthma) and other respiratory conditions in horses, characterised by constriction of the lower airways of the lungs. 

Clenbuterol administration can be associated with some immediate adverse effects such as an increased heartrate, sweating and muscle tremors. In the longer term, clenbuterol administration is associated with potentially adverse effects on bone strength, sweating, the immune system, and the heart muscle.


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.