A teenager who was arrested in connection with the supply of a drug known as "Rockstar" has been freed pending further investigation, the Crown Office said.
Seven people were treated in hospital over the weekend after apparently taking the tablets, which are thought to have been circulating in the Lanarkshire area.
The red or yellow-coloured pills were allegedly being sold as ecstasy.
Strathclyde Police said an 18-year-old man was arrested.
He was expected to appear at Airdrie Sheriff Court on Tuesday but a Crown Office spokesman said: "The procurator fiscal at Airdrie received a report concerning an 18-year-old male in connection with an incident on March 2, 2013.