Dyfed-Powys Police, Dyfed Drug and Alcohol Service (DDAS) and Hywel Dda University Health Board have issued a warning about the dangers of ecstasy, following a number of recent hospitalisations.
In the past month, several teenagers have been admitted to hospital in Pembrokeshire after taking ecstasy.
They have experienced problems including dangerously high heart rates, sweating, and in one instance a patient had to be put on a ventilator.
The most recent case was a 16-year-old girl who was taken to hospital last Wednesday, 13 December.
Police say she has now been discharged from hospital and is recovering at home.
Police say teenagers need to be particularly careful if offered MDMA (ecstasy) named Ikea, blue and yellow tablets branded with the Ikea logo, or Rolls Royce, which are pink tablets embossed with the Rolls Royce logo.
A number of Rolls Royce tablets were seized over the weekend in Brynamman, Carmarthenshire.