AJAX, Ont. - Durham region police are issuing a warning after three teens became ill -- one seriously -- while experimenting with a chemical compound purchased over the Internet.

Police say they were called to a residence in Ajax, Ont., early Saturday, where emergency personnel were already on the scene.

A 17-year-old youth was placed in intensive care after suffering seizures and vomiting after taking the drug.

Two other 18-year-old men in the basement of the residence were also taken to hospital, but they were not as ill.

Police say the victims had consumed a chemical compound with psychoactive effects that one of them bought over the Internet.

The department says people should be aware of the risks of consuming non-prescribed chemical compounds, especially those purchased online.