While the drug has been used for centuries overseas, it has only recently gained popularity in the U.S. as the opioid crisis has caused many to look to other alternatives for painkillers. As a substance that binds to the opioid receptors, some say kratom lacks the addictive or mind-altering effects of opioid-based painkillers. Some propose it could help wean those addicted to heroin and prescription pain killers off the drugs.