Warwickshire Police said several other people were also admitted to hospital after “suffering adverse effects” from the suspected ecstasy pills in the early hours of Saturday.
The force has now issued a warning about a red hexagonal pill named “red bull”, which the group are thought to have used, and urged anyone who has taken it to seek medical help.
The group had attended a drum and bass student event at The Assembly in Leamington but police say they may not have bought the drugs onsite.
Detective Superintendent Pete Hill said: “Our thoughts are with the family of the teenager, and specialist officers are currently supporting them.
“At this time we believe the tablet taken is a red hexagonal pill named ‘Red Bull’, which is believed to be MDMA, and we are concerned there may be others who have also taken this.
Source: Only Techno