Demerol is in a group of drugs called narcotic pain relievers & it is similar to morphine. Demerol is used to treat moderate-to-severe pain, is a fast-acting opioid analgesic drug.

Demerol came to international public attention in June 2009, when media reports linked it to the death of Michael Jackson. ABC News reported that Michael Jackson had been addicted to pethidine for 20 years, & had received an injection of it one hour before his death on June 25, 2009.

The drug Pethidine or meperidine, commonly referred to as Demerol but also referred to as:

• isonipecaine;
• lidol;
• pethanol;
• piridosal;
• Algil;
• Alodan;
• Centralgin;
• Dispadol;
• Dolantin;
• Petidin Dolargan
• Dolestine;
• Dolosal;
• Dolsin;
• Mefedina

In the US & Canada, it is more commonly known as meperidine or  Demerol.

source: (wikipedia.org, drugs.com)