– On a sunny November afternoon in this quiet college community, a steady stream of customers walks through the doors of a local cafe called Oasis for a cup of an increasingly popular herbal beverage. The menu offers coffee, black tea, beer, wine and pastries, but nearly everyone opts for a $5 mug of kratom.

A powder ground from the leaves of an indigenous Southeast Asian tree related to the coffee plant, kratom (Mitragyna speciosa) offers pain relief and mood enhancement, similar to prescription painkillers.

Advocates say the substance, which does not depress the respiratory system and therefore presents little to no overdose risk, could help reduce reliance on highly addictive prescription painkillers. Some addiction experts also argue the plant could be used in medication-assisted therapy for addiction.

Used for centuries in Indonesia, Malaysia, Myanmar, Papua New Guinea and Thailand, kratom was rarely taken in the U.S. until recently.

Now, with growing concerns about the dangers of prescription painkillers, an estimated 3 million to 5 million people are using kratom and reporting positive results. But worries that the unregulated plant product could be abused for its mild euphoric qualities and users could become addicted spurred federal officials to issue health warnings.

Alabama, Arkansas, Indiana, Tennessee, Vermont, Wisconsin and the District of Columbia have banned kratom, along with at least three cities — Denver, San Diego and Sarasota, Fla. Legislation was considered last year in at least six other states — Florida, Kentucky, New Hampshire, New Jersey, New York and North Carolina.

Animal studies have shown that kratom use may lead to addiction. But user surveys indicate that although the herb can be habit-forming, withdrawal symptoms are no worse than those encountered when quitting coffee, sugar or certain herbal supplements. Withdrawal symptoms typically last three to four days.

The Drug Enforcement Administration last year said it intended to classify the herbal supplement as an illegal Schedule 1 drug, along with heroin, LSD and marijuana. But after letters from Congress and a petition with more than 142,000 signatures, the agency put the proposal on hold.

Last month, Food and Drug Administration chief Scott Gottlieb issued a public health warning, citing 36 deaths in which kratom was present, but not necessarily the cause. About 50,000 Americans die of drug overdoses each year. In addition, the FDA, which has been seizing imports of kratom at U.S. ports since 2013, stepped up import enforcement.

The agency also cited a 10-fold increase in kratom-related calls to poison centers between 2010 and 2015 — from 26 calls to 263, out of roughly 2.2 million calls a year.

The American Kratom Association, a Colorado-based advocacy and lobbying organization, issued its own analysis of FDA data on adverse drug events, calling the kratom numbers “incredibly insignificant.”

At Oasis, owner Robert Roskind said the controversy has improved business by focusing attention on what he called a little-known plant with huge benefits and few drawbacks. “Except for the rare upset stomach or lightheadedness, it has helped nearly everyone,” he said.

The American Society of Addiction Medicine argued in comments to the DEA last year that the whole botanical product, like the powder sold at Oasis, should be made illegal to prevent people with addictions from trying to use it to recover.

At the same time, they recommended that what appears to be the plant’s primary active ingredients, mitragynine and 7-hydroxymitragynine, should remain legal so they can be researched for their pain relief and addiction treatment potential.