Police are investigating the circumstances surrounding the death of a 40-year-old man from Langwith.
Officers were called by staff at Kings Mill Hospital, Mansfield at 10.50am on Friday after the man arrived at hospital in cardiac arrest.
Police believe he may have taken amphetamine and M-CAT.
A second man, aged 18, also from the Langwith area had been taken to hospital he same day but his condition was not thought to be life threatening.
It is suspected he also took amphetamine and M-CAT with the 40-year-old man.
A 23-year-old man was arrested on suspicion of supplying drugs.
If you have information about drugs in your community contact Derbyshire police on 101 or Crimestoppers anonymously on 0800 555 111.