WASHINGTON (WOWO) — Federal officials are warning about the return of carfentanil, an extremely potent synthetic opioid originally developed as an elephant tranquilizer, amid concerns that dangerous fentanyl analogues are appearing in the nation’s illicit drug supply.

White House drug czar Sara Carter discussed the threat during an appearance on Fox News’ Hannity, warning that increasingly potent synthetic opioids can be mixed into illicit drugs without users knowing they are present.

Carfentanil is an analogue of fentanyl and was developed for use as a large-animal tranquilizer. Its extreme potency has made its presence in the illicit drug supply a particular concern for public health and law enforcement officials.

Carter also discussed the death of actress Hayden Panettiere in the context of the broader dangers posed by illicit synthetic opioids, while warning that new and increasingly dangerous drug analogues are emerging.

The concerns come as federal authorities continue targeting synthetic opioids and other substances entering the illicit drug market. The presence of fentanyl analogues can make an already unpredictable drug supply even more difficult for users to assess, particularly when substances are sold as other drugs.

Carfentanil is not approved for use in humans and is substantially more potent than fentanyl. Exposure can result in life-threatening opioid poisoning, including respiratory depression and death.

Federal officials have increasingly focused on emerging synthetic opioids as part of broader efforts to disrupt the illicit drug supply and identify new substances before they become more widespread.