The UCI says it provisionally suspended four Costa Rican riders this month who tested positive for "GW501516" at the Tour of Costa Rica last December. They are Vargas Barrantes, Mudarra Segura, Morales Castillo and Villalobos Azofeifa.
The drug is subject of a World Anti-Doping Agency health warning.
Last week, the UCI suspended European Championship track silver-medallist Valery Kaykov pending an investigation by the Russian cycling federation
Kaykov was tested on March 17, four days before WADA warned athletes not to use the endurance-boosting substance because of toxic side effects.
WADA was advised in 2009 to add the drug to the list of banned doping substances.