Pethidine or meperidine (often called Demerol in the United States) is a synthetic opioid - a man-made drug similar to morphine. It is a painkiller. It is used against moderate to severe pain. It can mix badly with other medicines, including muscle relaxants, some antidepressants, benzodiazepines, and alcohol.
Pethidine can be bad for people with liver disease, kidney disease, an enlarged prostate, trouble peeing, hyperthyroidism, asthma or Addison's disease. It can also be bad for people who have had seizures or epilepsy.