Your body would never get used to the perfect painkiller, says Susruta Majumdar, a chemist at Memorial Sloan Kettering Cancer Center. So unlike the case with common opioids such as morphine or Oxycontin, you would not need to take ever-increasing doses to relieve the same amount of pain. The ideal analgesic would not have the high risk of addiction, withdrawal or fatal respiratory slowdowns that have turned opioid abuse into a massive epidemic. The holy grail of painkillers would not induce the seductive euphoria of common opioids or their less-pleasant side effects like itching or constipation.

A painkiller with just one of these properties would be great, but Majumdar thinks he has stumbled onto a class of chemicals that might have them all. They are found in kratom, a plant that the U.S. Drug Enforcement Administration intends to effectively ban from the U.S. in an emergency move as early as September 30. Without legal access to it, research on some of the most promising leads for a better painkiller may grind to a crawl.

Kratom comes from the Mitragyna speciosa tree native to parts of Southeast Asia, where people chew the leaves for a light, caffeine-like jolt of energy or as a traditional medicine for ailments ranging from diarrhea to pain. Kratom has been illegal since 1943 in Thailand, where it is believed to be addictive. Case studies have suggested that suddenly stopping regular kratom use may lead to withdrawal symptoms—but they are widely considered milder than those associated with opioids.   MORE