The horses tested positive for capsaicin, the ingredient that gives peppers their fire.
At a press conference FEI chairman of jumping Alexander McLin said: "It is a serious blow to the sport. We are very well aware of the implications to jumping and equestrian sport in general."
Four riders, including Lynch, were suspended from the competition. Three were to have taken part in last night's individual jumping final.
Horse Sport Ireland has confirmed that they submitted a urine sample from the horse to a voluntary screening testing process made available by the FEI on the horse's arrival in Hong Kong and the results of this test were negative.
Lantinus has also been tested on numerous occasions, including following many of its recent victories, and has tested negative on all these occasions.
Under FEI rules, capsaicin is a class A prohibited substance for its pain-relieving qualities. It is classified as a doping agent banned due to its hyper-sensitising properties. It has always been prohibited, but only in the last couple of years has technology has been developed to detect it because it disappears quickly from a horse's system.
Product literature on Equi-Block, from EquiFlite Techbologies, says the product "will not test positive." It contains 0.025% of capsaicin, as well as Deionized Water, Chamomile Extract, Carbomer 940, Polysorbate 20, Triethanolamine, Propyl Gallate, Methylparaben, Imidazolidinyl Urea, and Propylparaben.