Wildnil is the brand name for the ultrapotent opioid carfentanil, it is used in veterinary medicine to anesthetize large animals such as elephants and rhinoceroses, usually delivered via a tranquilizer dart. Carfentanil is the most potent opioid produced commercially, it is an analog of fentanyl and is 100 times as potent, it has 4,000 times the potency of heroin and 10,000 times the potency of morphine; the median lethal dose of carfentanil in humans is 2 micrograms (0.02 milligrams). Carfentanil is also used illicitly, it is sometimes cut with heroin so that longtime users with a high tolerance can get a better high, but due to its high potency even regular heroin users can easily overdose on carfentanil.