Four types of synthetic opioids, including an elephant tranquilizer, are to be added to China's list of controlled substances, as authorities crack down on a new generation of illegal narcotics.

Starting March 1, four fentanyl-based medications will be put on the List of Nonpharmaceutical Narcotic Drugs and Psychotropic Drugs Under Control, taking the total number of controlled substances to 134, the Ministry of Public Security said on Thursday.

Fentanyl is a synthetic opioid that is about 10,000 times more powerful than morphine and is identified as a new psychoactive substance, China's so-called third generation of drugs.