Kratom Long-Term Effects: What the Research Can and Cannot Tell You

By Kemal Whyte, founder and CEO of Rebel X Brands.
Published 6 October 2026.

On the federal record, kratom long-term effects come down to one sentence from the National Institute on Drug Abuse: "Long-term health and safety effects are not well understood." Everything below is detail on why that is still true in October 2026.

There are two dishonest ways to answer the question. One takes studies of traditional leaf users in southern Thailand and Malaysia, which mostly found no clinically significant differences on blood tests, and hands them to someone buying a concentrated extract in a US shop as if they were about him. The other presents single case reports as what years of use do to everyone. I sell kratom products, so the first is the one my interest pulls toward.

So where a finding comes from one patient, I say so. Where it comes from men chewing leaf or drinking leaf juice in Southeast Asian communities, I say that too, because that is where long term kratom use has mostly been studied.

What the agencies say about the long-term effects of kratom

NIDA's kratom page, last modified on 11 March 2026, on the long term:

Long-term health and safety effects are not well understood. Because kratom research is relatively new compared to research on more widely used drugs, there is little evidence to determine how kratom use may affect someone over time. Case reports do show regular, long-term, kratom use in large amounts may be associated with serious liver problems. These cases appear to occur unpredictably in a small minority of people who use kratom, and it is unclear what role other substances and underlying health conditions may play.

The National Center for Complementary and Integrative Health (NCCIH), on a page last updated in April 2022: "The long-term effects of kratom use are not well understood. There have been reports that long-term use of large doses of kratom may cause serious liver problems in some people." Both name the liver. Neither offers a rate.

FDA's page, FDA and Kratom, current as of 2 December 2025, does not use the phrase long-term at all. It warns: "FDA has warned consumers not to use kratom because of the risk of serious adverse events, including liver toxicity, seizures, and substance use disorder (SUD)." And it concedes there are "few published reports from well-designed scientific studies where kratom was administered to humans."

None of the three says kratom is safe over the long term, and none puts a number on any long-term risk. Anyone telling you the agencies have settled this, in either direction, has not read them.

The liver: rare, graded a likely cause, usually weeks after starting

LiverTox, the National Institutes of Health database on drug-induced liver injury, last updated its kratom entry on 3 April 2020, so read it as a 2020 document. It calls kratom-linked liver injury rare, and its causality grade reads, verbatim, "Likelihood Score: B (likely cause of clinically apparent liver injury)." That is a judgment about cause across the published cases. It is not a frequency. Then the timing:

Chronic use of kratom recreationally has been associated with rare instances of acute liver injury. The onset of injury is usually within 1 to 8 weeks of starting regular use of kratom powder or tablets, with symptoms of fatigue, nausea, pruritus and dark urine followed by jaundice.

The US Drug-Induced Liver Injury Network reported 11 cases attributed to kratom in 2021. All developed jaundice, with a median latency of 14 days; "most required hospitalization and all eventually recovered." Its conclusion: "Kratom can cause severe liver injury with jaundice."

So the clinical series describe injury that usually starts weeks after regular use begins, while NIDA and NCCIH speak of long-term use in large amounts. I give you both in their own words, because neither "years of use wreck the liver" nor "the risk is only at the start" is what the record says. Two more details from LiverTox: the cause "is unknown", and its description names kratom powder or tablets. Not fresh leaf.

The long-term user studies, and who was in them

The best human data on years of use come from southern Thailand and Malaysia. The paper listed on Johns Hopkins' research portal, by Saingam and colleagues in 2023, ran three community surveys from 2011 to 2015 among 1,118 men from 40 villages, not all of them followed throughout. Its conclusion cuts both ways: "Regular long-term chewing of fresh kratom leaves was not related to an increase in common health complaints, but may pose a drug dependence risk."

The largest laboratory comparison I found was published in Scientific Reports on 16 January 2026: 285 registered users and 296 non-users in a sub-district of Surat Thani province where a 2017 community charter permits use. It reports "no clinically significant differences were observed in hepatic or hematological parameters", and no clear dose-response relationship for organ toxicity, "although higher consumption was associated with altered renal markers."

Now look at who was compared. Users were 78.6% male, against 29.7% of non-users. 54.0% smoked, against 13.2%. Use was self-reported, and "the kratom products consumed by participants were not chemically analyzed". The authors say their cross-sectional design "fundamentally precludes the establishment of a temporal sequence or definitive causal inference".

The Malaysian studies are smaller and stricter. A 2020 study in PLOS ONE compared 100 regular users with 100 non-users, all men, and excluded anyone with other illicit drug use, psychiatric illness or medical illness. Liver tests were within normal range. Cholesterol is a mixed picture: a 2018 study of 58 users and 19 controls found HDL and LDL above the reference range in users, while the 2020 authors' findings "suggest regular kratom consumption was not linked to elevated serum lipids, except when there is a higher frequency of daily kratom intake." Small samples that disagree, and neither can show cause, so I will not tell you kratom raises or lowers cholesterol.

Two more are worth knowing. A 2018 study of 19 regular users, with no control group mentioned in its abstract, found tea or juice use over more than two years "was not associated with testosterone impairing effects in humans." A 2019 study of 70 users and 25 controls found them "comparable on all neuropsychological domains", though heavier daily use went with poorer scores on one memory task. One sample each, one point in time. Every study in this section is of leaf or leaf drinks in Thailand or Malaysia, not a US powder, extract or shot.

Heart rhythm: one comparison and one case series

Two pieces of Malaysian work are easy to merge, and should not be. The first compared 100 regular users with 100 controls who used no drugs, all men. As two of its authors summarized it in a 2021 review, users had higher odds of sinus tachycardia, 8% against 1%, and more than six years of use went with higher odds of a borderline QTc interval but not of a prolonged one. I could not read that study at source, so those figures are its authors' summary.

The second is a case series: nine men in Penang who had used kratom daily for the past 12 months, and no control group. Four had a prolonged QTc, and those with prolonged QTc had higher serum mitragynine. The authors thought the prolonged QTc "appeared to be dose dependent" and cautioned that the association "may not indicate the causative effect". Nine men. A signal worth studying, not a rate.

The laboratory work behind the QT concern was done in cells, and the same authors' review says in vitro findings "should not be exclusively extrapolated to represent cardiotoxicity risk in humans". Neither "kratom prolongs QT" nor "kratom is easy on the heart" is supported.

Dependence: established, and measured in different ways

On 14 September 2026 I wrote, in my column on who gets the withdrawal, that physical dependence and an opioid-like withdrawal syndrome in regular users are established, citing the Massachusetts and Connecticut health departments. I have not changed my mind. That is two state health departments, though, not the federal institute. NIDA is more cautious:

Studies suggest people may experience mild to moderate withdrawal symptoms when they stop regular kratom use, but more research is needed to understand to what extent people develop substance use disorder symptoms related to kratom.

NCCIH says "kratom itself may have the potential to be addictive". FDA says "Cases of kratom-related SUD have also been observed", with cravings, tolerance and withdrawal on stopping among the criteria met, though "a well-designed human abuse potential study has not been conducted". In the Thai villages, people with high dependence scores were more likely to experience intense withdrawal, which developed 1 to 12 hours after their last use.

How common is it? That depends on who was asked, and how.

Figure	Who was asked	Measured with	Not this
More than half severe, 45% moderate.	293 regular users in three northern Malaysian states; published 2014.	Leeds Dependence Questionnaire.	A DSM-5 diagnosis.
56 people, 2%, moderate or severe.	2,798 users, anonymous online survey, 2017.	DSM-5 criteria.	A rate for all US users.
344 people, 12.3%, any severity, most of them mild. The review counts 68 moderate or severe; the survey's abstract says 56.	The same survey, as a 2024 review reports it.	Past-year use disorder threshold.	A contradiction of the 2%: it counts mild cases too.
525 people, 25.5%, any severity, mostly mild or moderate.	Online nonprobability sample of 2,061 current consumers, 2023.	DSM-5 criteria adapted for kratom.	One in four users addicted.
66.7%.	357 daily or near-daily users.	Use disorder criteria, met mostly through withdrawal, tolerance, using more than intended and craving.	Occasional users. Interference with obligations was rare.

Rows three and five are as the 2024 review linked below reports them. Read the instrument before the number. The Malaysian survey used the Leeds Dependence Questionnaire and two scales built for marijuana, not DSM-5 criteria, so its "severe Kratom dependence problems" are not a diagnosis. The US surveys were anonymous, online and self-selected, and the 2023 one describes its own "nonprobability sampling". As I wrote in my September column, it "is not a population prevalence estimate".

Nor can the climb from 12.3% to 25.5% be read as a trend. A 2024 review in Current Psychiatry Reports says so: "Sampling differences preclude conclusions about whether the higher rate of cases in the second study represents a true increase." One of its three authors "has served as a paid scientific advisor to the International Plant and Herbal Alliance and The Kratom Coalition" and is an expert witness in kratom cases; the other two work in NIDA's own research program. It also says kratom "can lead to life-disrupting addiction manifestations in a small but nonnegligible proportion of consumers". Dependence turns up in the village studies and the US surveys alike, measured differently every time.

Single cases: hormones, thyroid and sodium

Some long-term harms you will see cited rest on one patient each, and a case report is not a rate.

In 2018, clinicians described a 42-year-old man whose prolactin was above its reference range and testosterone below it while he used kratom; after he stopped, the report says, both "had returned to normal". He had not mentioned kratom at his first visit. The report does not say how much he used or for how long, so it says nothing about long-term use. The Malaysian study above, of 19 tea or juice drinkers, found no testosterone impairment. Neither is a rate. There is also a 2011 case report on the thyroid, which I could not read at source.

In 2025, Annals of Internal Medicine: Clinical Cases described a patient with long-term daily kratom use who developed altered mental status and focal neurologic deficits with hyponatremia one week after abruptly stopping. It came after stopping, and one case cannot say why. I read only the abstract, so I cannot give the patient's age, the amounts or the outcome. The authors' lesson was for clinicians: "the necessity of obtaining a comprehensive history of all regularly consumed medications and supplements".

My advice, which is mine and not an agency's: if you use kratom regularly, or plan to stop, tell whoever treats you, and name the product. The 2018 patient, at first, had not.

Contaminants: what FDA's 2019 tests projected

The other long-term worry is what can ride along with the plant. In 2019 FDA reported laboratory tests of 30 kratom products and found "significant levels of lead and nickel at concentrations that exceed safe exposure for oral daily drug intake." It projected:

Based on these test results, the typical long-term kratom user could potentially develop heavy metal poisoning, which could include nervous system or kidney damage, anemia, high blood pressure, and/or increased risk of certain cancers.

Read the verbs. "Could potentially develop" is a projection from product testing, reported in 2019, not a count of people found poisoned. NIDA adds a sentence sellers should not hide behind and critics should not skip: "researchers and regulators have found similar instances of contamination in many other products marketed as herbal supplements." Which brings me to the biggest problem in this literature.

Why the leaf studies do not describe a US powder, extract or shot

The reassuring blood tests come from people chewing fresh leaf or drinking leaf juice in Thai and Malaysian communities. A 2024 review of kratom research needs puts the gap in one line: "fresh leaf made decoctions and leaf chewing are common in Southeast Asia but not the United States".

The differences stack up. Three Malaysian samples were all men and the Thai surveys men only; the 2026 study had 61 women among its users. Two Malaysian studies excluded people using other drugs or living with illness, so their users were selected to be well. And a comparison of current users with non-users leaves out anyone harmed badly enough to stop, because they are no longer in the user group. That last point is my reading of the design, not a finding of any paper, but it is why "no clinically significant differences" is a different sentence from "safe".

Then the products. NIDA: "Importantly, kratom products vary, so effects are difficult to predict." The psychiatry review notes that kratom "is increasingly being sold in concentrated formulations not reflective of the whole-leaf kratom products". And FDA says the results of its own human studies "will need to be considered in relation to the many and varied kratom-related products available to consumers".

My companies sell powder, capsules, extracts and extract shots. Those are not what the village studies looked at, and I would be misleading you if I let a blood test from a Thai village stand in for a customer of mine.

What I could not find anyone studying

I looked for a prospective study that recruited US users of powders, capsules, extracts or shots, measured them at the start and followed them for years. I did not find one. That is a search result, not proof that none exists; if you know of one, I want to read it. Every Southeast Asian study above is cross-sectional or a case series, apart from the repeated Thai surveys, and none measured anyone before they started.

The researchers list the gaps themselves. The 2026 Thai authors: "Prospective, longitudinal studies are urgently needed". The 2020 Malaysian authors recommend "a multicenter, prospective design (i.e., a cohort study)". A 2022 narrative review: "Kratom-related research for U.S. populations is still in its infancy". On treating kratom use disorder, the psychiatry review found "no randomized controlled trials, or even long-term outcome studies".

FDA describes two human studies: a single ascending dose study, whose manuscript its researchers have submitted to a peer-reviewed journal, and a human abuse potential study, for which it awarded a grant in September 2024. Neither, on FDA's description, follows people over years.

Opinion: what I take from this, as a seller

First, the honest summary is the agencies' one: long-term effects are not well understood. The best long-term data describe mostly men using leaf in Southeast Asian communities, and show few differences on blood tests, a dependence risk, and heart questions that nine men cannot answer.

Second, nobody selling powders, extracts or shots in the US, me included, can point to a long-term study of what we sell, as far as I can find. I have argued before that this industry should fund the science. A prospective study of US consumers, with the products tested and blood drawn at the start, is the study I mean, and it should be run by people we do not pay.

Third, until then the useful things are dull: tell your clinician, as I advised above, and report problems. FDA "encourages health care professionals and consumers to report any adverse reactions to the FDA's MedWatch program or the Safety Reporting Portal." If a page, including one of mine, uses the Thai or Malaysian studies to tell you an extract is fine over years, send it to me. My other columns on this trade are on Unfiltered.

Questions about kratom long-term effects

What are the long-term effects of kratom?

Not well understood, in the words of both NIDA and NCCIH. Studies of traditional users in southern Thailand and Malaysia, mostly men using leaf, found no clinically significant differences in liver tests or blood counts, but did find signs of dependence. They cannot speak for US powders, extracts or shots, and I have found no long-term study of those.

Does long-term kratom use damage the liver?

LiverTox calls kratom-linked liver injury rare, grades kratom a likely cause of clinically apparent liver injury, and says onset is usually within 1 to 8 weeks of starting regular use. NIDA says case reports show regular, long-term use in large amounts may be associated with serious liver problems. Questions about your own liver belong with a clinician.

Is kratom addictive with long-term use?

FDA says cases of kratom-related substance use disorder have been observed, and NCCIH says regular users may experience withdrawal if they stop. I have written that physical dependence in regular users is established, citing two state health departments; NIDA is more cautious. In self-selected online surveys using DSM-5-based criteria, 2% met moderate or severe criteria in 2017 and 25.5% met criteria at any severity, mostly mild or moderate, in 2023; the two cannot be read as a trend.

Do the Thai and Malaysian studies apply to kratom sold in the US?

Not directly. Their users chewed fresh leaf or drank leaf juice, were mostly or entirely men, and two Malaysian studies excluded people using other drugs. A 2024 review notes that leaf chewing and fresh leaf decoctions are common in Southeast Asia but not in the United States. None of them measured use of powders, extracts or shots.

Disclaimer: This guide summarizes research and agency pages as they read on 6 October 2026, and links to primary sources so you can check them. Studies, agency pages and case counts change. It is general information, not medical or legal advice, and no substitute for a clinician. Sections marked as opinion or advice are the author's own, and the author holds commercial interests in botanical brands. Nothing here is a health claim, and statements about botanical products have not been evaluated by the Food and Drug Administration.

Written by Kemal Whyte, founder and CEO of Rebel X Brands, Austin, Texas.