Officers say one of their friends called police from Mill Lake Park at about 6:45 p.m. Sunday to report that the youths were having a bad reaction to a drug.
The caller said the three were vomiting and convulsing.
Police say they arrived to find a 19-year-old man and a 15-year-old girl unresponsive, and a 17-year-old girl who was semi-conscious.
All three remain to hospital and are expected to survive.
Police have issued a reminder that GHB and other street drugs can contain dangerous and unknown additives.
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