Police have raised concerns about the increasing use of a "legal high" ahead of the RockNess music festival at Dores on the shores of Loch Ness.
The Association of Police Officers in Scotland (Acpos) said NRG-1, or Energy-1, was being marketed on websites as legal to use.
But the organisation said tests of samples had found the substance contained class B drugs.
Acpos said police would "rigorously target" drug misuse at RockNess.
The music festival near Inverness will be held on Friday, Saturday and Sunday.
The event attracted more than 35,000 people last year.
Acpos said in recent months there has been a rise in the number of cases of NRG-1 misuse across the UK.
It said Dr Roland Armes, consultant in emergency medicine at Aberdeen Royal Infirmary, had reported a rising number of patients who had taken a substance labelled as NRG-1.
Det Supt Willie MacColl, of the Scottish Crime and Drug Enforcement Agency said: "Users can never be sure what they are taking and this could lead to severe consequences.
"The adverse effects on an individual's health are not known and there is a real potential for short term and long term harm from these substances."