Detectives held the teenager after Jack Blades, 16, collapsed after apparently taking a Mortal Kombat pill.
Jack, of Airdrie, North Lanarkshire, was in a coma last night and health chiefs said his condition was stable.
The boy who was arrested had been expected to appear at Airdrie Sheriff Court. But prosecutors revealed he had been freed pending further enquiries.
A Crown Office spokesman said: "Following careful consideration, the accused was liberated from custody pending further enquiries and did not appear in court."