Mitragyna speciosa

• 1. Introduction

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  In Thailand, the leaves of Mitragyna speciosa were once described as "used as a snack to receive guests and was part of the ritual worship of ancestors and gods". That same leaf, known as kratom, is now restricted across much of the world. It is chewed, brewed into tea, powdered into capsules and argued over in legislatures. How did a bitter leaf from a Southeast Asian tree become both a gesture of hospitality and a target of drug law? What do researchers actually know about what it does inside the body? And why did Thailand, after decades of treating it as a narcotic, reverse course and forgive thousands of people convicted over it?

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• 2. The Tree

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  In 1839, a Dutch colonial botanist named Pieter Korthals first formally described the plant and called it Stephegyne speciosa. Over the following years it was renamed and reclassified several times. George Darby Haviland settled the question in 1859 by providing the name and classification still used today.

  The tree belongs to the Rubiaceae family and grows in Cambodia, Thailand, Indonesia, Malaysia, Myanmar and Papua New Guinea. It stays green all year and can reach 25 m in height. The trunk is generally straight and may grow to 3 ft across, with smooth grey outer bark.

  The leaves are what people care about. They grow in opposite pairs, are ovate-acuminate in shape, and are dark green and glossy on top. A leaf can run past 14-20 cm in length and 7-12 cm in width, with 12 to 17 pairs of veins.

  At the ends of the branches, deep yellow spherical flower clusters appear in groups of three. Each flower has a calyx-tube about 2 mm long with five lobes. The corolla-tube measures 2.5-3 mm. For most of its history, though, nobody looked at the flowers. The attention went to the leaves, and to the people who chewed them.

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• 3. Working Leaves

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  A report from 1836 describes kratom being used in Malaysia as a substitute for opium. In Thailand during the 19th century it served the same purpose. This was one of the earliest recorded roles for the leaf outside its home forests.

  In the places where the tree grows, kratom became a tool for people doing tiring work. Laborers in demanding or monotonous jobs used it to hold off exhaustion, lift their mood and dull pain. The leaves are bitter, so they are generally combined with a sweetener.

  Traditional medicine gave the leaves many jobs. Chewed, they were meant to ease muscle and joint pain and to raise energy, appetite and sexual desire, much like khat and coca. The leaves or extracts were applied to wounds and used as a local anesthetic. People also turned to them for coughs, diarrhea and intestinal infections, and in Thailand as a dewormer.

  Today people chew the leaves, steep them as tea, swallow powder in capsules or pills, or use liquid extracts. Smoking is rare. Different varieties carry different proportions of alkaloids such as mitragynine.

  The oldest use has found a modern echo. Because kratom withdrawal is often reported as milder than withdrawal from conventional opioids, some people try it to manage opioid use disorder. No clinical trials support this. A review by Stanciu and colleagues found too little evidence to say whether kratom is harmful or whether it works as harm reduction. Some reviews suggest lower risk of dependence or overdose than with standard opioids, while others stress that kratom withdrawal can itself be severe.

  Researchers have studied the plant in cells and in animals, but no clinical trials have been run in the United States. Kratom use has not been shown to improve mental health, though preliminary work is looking at possible antipsychotic and antidepressant properties.

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• 4. Alkaloid Chemistry

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  At least 54 alkaloids have been identified in kratom. The two that matter most are mitragynine and 7-hydroxymitragynine, often shortened to 7-HMG. Both are partial agonists of the mu-opioid receptor, meaning they switch it on only partway. Researchers still dispute many of their other effects despite substantial study, and other alkaloids may add to the picture.

  In one study, mitragynine made up 12% of the leaf by weight in Malaysian samples, against 66% in Thai samples. The 7-hydroxymitragynine fraction was only about 2%. Yet 7-HMG appears to grip the mu-opioid receptor more tightly than mitragynine does.

  The pair behave differently from traditional opioids in one notable way. They show functional selectivity and do not trigger the beta-arrestin pathway, which is partly responsible for respiratory depression, constipation and sedation. Both compounds cross the blood-brain barrier easily.

  Mitragynine also appears to inhibit the enzyme COX-2 and to block two kinds of calcium channel. It interacts with serotonin receptors called 5-HT2C and 5-HT7, with D2 dopamine receptors and with A2A adenosine receptors. It also stimulates alpha-2 adrenergic receptors, as the sedative dexmedetomidine and the anxiety drug clonidine do. That action might explain why kratom is dangerous alongside other sedatives. Another alkaloid, rhynchophylline, blocks NMDA receptors.

  Some users find kratom stimulating. That effect probably does not come from the usual stimulant mechanisms, and it is not universal.

  Beyond alkaloids, the leaf produces saponins, iridoids, triterpenoids such as ursolic acid and oleanic acid, and flavonoids including apigenin and quercetin. In cells and animals some of these show pain-blocking, anti-inflammatory and antidepressant-like effects. Evidence is not sufficient to support clinical use in humans.

  Typical drug screening tests do not detect the plant's compounds. Specialized testing can find them. Blood mitragynine in recreational users is expected to fall between 10 and 50 micrograms per liter, and labs measure it with liquid chromatography-mass spectrometry. In laboratory experiments, kratom extracts also inhibited the liver enzymes CYP3A4, CYP2D6 and CYP1A2, which raises a strong chance of interactions with other drugs.

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• 5. Recreational Use

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  A 2007 survey in Thailand asked people aged 12-65 about kratom. Lifetime use was 2.32%, past-year use 0.81% and past-30-day use 0.57%. That made it the most widely used recreational drug in the country.

  The experience depends on dose. At low doses kratom produces euphoria comparable to coca. At higher doses the effects turn opioid-like. Effects typically begin within five to ten minutes and last two to five hours. Anecdotal reports describe more alertness, talkativeness, sociability, positive mood and greater capacity for work.

  In the United States, common doses are 2-6 g of dried leaf, and doses above 8 g are relatively uncommon. Potency varies greatly between products, so no standard dosing system exists. Kratom sold in that market has also been mixed with other psychoactive drugs such as caffeine and codeine.

  Starting in the 2010s, young people across Southeast Asia, especially in Thailand, embraced a tea-based cocktail called "4×100". It combines kratom leaves, cough syrup, Coca-Cola and ice. Around 2011, people who drank it were viewed more negatively than traditional kratom users, though not as negatively as heroin users. By 2012 the cocktail was a severe problem among youth in three provinces along the border between Malaysia and southern Thailand.

  In the United States, kratom was sold through head shops and over the Internet. Use increased rapidly between 2011 and 2017. A 2020 survey and the U.S. Drug Enforcement Administration both report that people use it against pain, anxiety, depression or opioid withdrawal. By 2020, an estimated 15 million people worldwide used kratom, although good data are lacking. Many of the harms below come from this period of rapid growth.

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• 6. Risks And Harms

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  In July 2016, the Centers for Disease Control reported 660 exposures to kratom logged by U.S. poison control centers between 2010 and 2015. Of these, 162 (24.5%) had minor outcomes, 275 (41.7%) moderate outcomes and 49 (7.4%) major, life-threatening ones. The single death involved kratom plus an antidepressant and a mood stabilizer.

  A 2019 review of 935 exposures over seven years listed agitation in 18.6%, a racing heart in 16.9% and drowsiness in 13.6%. Seizures and withdrawal symptoms each appeared in 6.1%. It also reported two deaths and four cases of neonatal abstinence syndrome.

  A 2019 report from the American Association of Poison Control Centers counted 1807 exposures, a 52-fold increase between 2011 and 2017. Of the incidents, 32% needed admission to a health care facility. Cases involving several substances produced more hospitalizations, and 11 deaths, two of them from kratom alone. Fentanyl and its analogs were the substances most often found with kratom in those who died.

  In all, 44 U.S. deaths between 2011 and 2017 were kratom-related, though many cases lacked enough information to assess. Over 18 months in 2016 and 2017, 152 overdose deaths involving kratom were reported, with kratom the primary agent in 91 and the only agent in 7. In Sweden, nine deaths in 2010-11 were tied to Krypton, a mixture of kratom, caffeine and O-desmethyltramadol.

  Contamination is a separate hazard. From October 2017 to February 2018-28 people in 20 states fell ill with salmonella, and whole genome sequencing suggested a common kratom source.

  Dependence can set in quickly. In vulnerable people, tolerance appears by three months, and dose increases of four- to ten-fold may be needed within the first few weeks. In a survey by Stanciu and colleagues, 25.5% of kratom consumers reported symptoms consistent with a substance use disorder. People who already had another such disorder had 2.83 times the odds of kratom addiction. Relapse risk after stopping can reach 78-89% at three months. Withdrawal brings loss of appetite, insomnia, muscle spasms, yawning, fever, restlessness, anger and sadness.

  The liver can suffer too. Reported liver injury had a median latency of 20.6 days, with abdominal discomfort, dark urine, itching and jaundice. Many users never develop it, and no one knows who is at higher risk.

  Infants born to mothers who used kratom during pregnancy may show jitteriness, poor feeding, irritability and sleeplessness. Some need hospital care and weaning with morphine. A 2018 review found that kratom alkaloids do not induce respiratory depression, though the FDA still lists it as a concern.

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• 7. Laws Around The World

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  On the 3rd of August 1943, Thailand's Kratom Act 2486 took effect and made planting the tree illegal. Use had risen when opium became very expensive, and the government was trying to take control of the opium market. In 1979, kratom was placed with cannabis in Category V of a five-category narcotics system. Between 1987 and 1992 it accounted for less than two percent of narcotics arrests.

  The Thai government considered legalizing recreational use in 2004, 2009-2013 and 2020. In 2018 Thailand became the first Southeast Asian country to legalize kratom for medical purposes. In 2021 it fully legalized the plant and removed it from Category V. More than 12,000 people convicted of kratom offences received an amnesty.

  Neighboring Malaysia took the opposite path. There kratom is called ketum or Biak, and the Poisons Act 1952 forbids using, selling or possessing it. Use remains widespread in the north and on the East Coast, because the tree grows natively and tea is easy to find. Some parties want the Dangerous Drugs Act applied instead, with heavier penalties.

  Indonesia changed direction in 2024. A revision to a Ministry of Trade regulation legalized production and export of kratom leaves. That September, another ministry said it would build downstream industries for kratom exports.

  As of 2018, kratom was a controlled substance in sixteen countries. Australia prohibits it. New Zealand treats it as a prescription medicine and bans it from herbal remedies under the Medicines Act 1981. Health Canada disallows marketing for ingestion but allows other uses such as incense.

  In Europe, Denmark, Latvia, Lithuania, Poland, Romania and Sweden control the plant, as do Bulgaria and Norway. Ireland made it a Schedule 1 drug in 2017, and the United Kingdom bans its sale under the Psychoactive Substances Act 2016. The Czech Republic went the other way, making regulated sales legal from July 2025.

  Japan prohibits manufacture, import, possession and use. Argentina banned it in 2017 and Chile in 2021, while Brazil listed it as a New Psychoactive Substance in 2020. In 2021, the World Health Organization's drug dependence committee declined to recommend a critical review and said to keep kratom under surveillance.

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• 8. The American Fight

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  In 2014, the U.S. Food and Drug Administration banned imports of kratom because evidence of its safety was lacking. The Drug Enforcement Administration had already stated in 2013 that kratom has no legitimate medical use. Then, on the 30th of August 2016, the DEA announced plans to place its active materials in Schedule I, calling it an imminent hazard to public safety.

  The protest was loud. A group of 51 members of the House of Representatives and a group of nine senators each wrote to the acting DEA administrator, Chuck Rosenberg. Around 140,000 people signed an online White House petition. A DEA spokesman answered that the agency could not rely on public opinion and anecdotal evidence and had to rely on science. In October 2016 the DEA withdrew its notice and opened a comment period that ran to the 1st of December 2016.

  By July 2016, Alabama, Arkansas, Indiana, Vermont and Wisconsin had outlawed kratom, and the U.S. Army forbade soldiers from using it. According to the International Narcotics Control Board, authorities encountered 55 tons of it between February 2014 and July 2016, roughly 50 million individual doses.

  The FDA pressed on. In November 2017 it said there was no reliable evidence that kratom treats opioid use disorder. In February 2018, Commissioner Scott Gottlieb described further opioid-like properties and said it should not be used for medical treatment or recreation. On the 4th of April 2018, the FDA issued the first mandatory recall in its history, over salmonella in products made by Triangle Pharmanaturals and sold as Raw Form Organics. In 2019 it repeated that kratom was unapproved, possibly unsafe and subject to an import alert.

  Critics pushed back. In 2021, former Acting Commissioner Brett Giroir said the recommendation to schedule kratom was rejected because of "embarrassingly poor evidence and data." The American Kratom Association and researchers including Walter Prozialeck also criticized the FDA's position. Gottlieb kept defending it. Federal scheduling efforts ultimately failed.

  The fight then moved to states and cities. In 2016, San Diego and Oceanside banned kratom. In 2025, eight Massachusetts communities followed, including Belchertown, Canton, Chelmsford, Dracut, Kingston, Lowell, Marlborough and Northampton. On the 13th of August 2025, Florida Attorney General James Uthmeier announced an emergency rule placing 7-hydroxymitragynine in Schedule I, with no exclusion for the plant, which holds only low amounts of it. Ohio temporarily banned kratom products from the 12th of December 2025 for 180 days. California's administration warned retailers that selling it was illegal, Los Angeles County banned it, and Orange County restricted products with more than 2% 7-hydroxymitragynine. In early 2026, bills to ban kratom were introduced in Iowa, Nebraska and South Dakota.

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