Fentanyl is 50 times more potent than heroin and 100 times more potent than morphine. There are also countless types of fentanyl analogues, which are similar in chemical structure to fentanyl, but can be even more potent. Carfentanil, the most powerful fentanyl analogue detected in the United States, is estimated to be 10,000 times more potent than morphine. Although commonly used as a tranquilizer for elephants and other large mammals, drug traffickers mix carfentanil or other fentanyl-related substances with heroin or other illicit drugs to make the drugs stronger.