Young revellers were rushed to hospital after taking the Class A drug 2CB.
Ten people became ill in the early hours of Saturday morning after taking the ‘club drug’ during two separate house parties in Potten End and Croxley Green.
Some had to be taken to hospital by ambulance and five young people, aged from their late teens to early 20s, from the quiet village between Berkhamsted and Hemel Hempstead needed treatment.
Det Insp Paul Doran said: “It is important we remind members of the public of the serious risks of taking illegal drugs.
“You could be dicing with death or suffer life-changing internal injuries. If you become unwell having taken this please ensure you go to hospital immediately.
“Drugs have no place in our communities and investigations are currently on-going to find the source of the drug. Anyone involved in any offences will of course be dealt with.
“I would urge anyone with any information about the supply of this drug to contact Herts Police on 101 or Crimestoppers anonymously on 0800 555 111.”
Three people have been arrested on suspicion of supplying drugs. They are an 18-year-old man from Watford, a 20-year-old woman from Leavesden and a 20-year-old man from Croxley Green. The trio have been bailed by police until Saturday, June 8.
The drug 2CB is quite rare in the UK compared to others and is sometimes sold as ecstasy. It is made in illegal labs as far away as India and Thailand and usually comes as a tablet or capsule.