What Is MIT in Kratom? Mitragynine Explained

MIT is shorthand for mitragynine, the most abundant psychoactive alkaloid in kratom leaves. It accounts for roughly 1 to 6 percent of the dried leaf by weight, making it the compound most responsible for kratom’s effects on mood, pain perception, and energy. Mitragynine interacts with opioid receptors in the brain, but it does so in an unusual way that sets it apart from conventional opioids, and that distinction is at the center of ongoing scientific debate about kratom’s risks and therapeutic potential.

How Much Mitragynine Is Actually in Kratom

Kratom products are not standardized, so the amount of mitragynine you get in any given bag of powder or capsule can vary enormously. One analysis of commercial products sold in the Chicago suburbs found mitragynine concentrations ranging from about 4 to 62 milligrams per gram of product, a roughly 16-fold difference from the lowest to the highest sample.¹ That variability matters because someone switching brands or even batches could unknowingly double or triple their mitragynine intake without changing the number of capsules they swallow.

The raw leaf itself typically contains mitragynine at levels between 1 and 6 percent of dry weight, though the exact concentration depends on the tree’s growing conditions, the maturity of the leaves, and how they were dried and processed. A second alkaloid, 7-hydroxymitragynine, is present at trace levels, usually between 0.01 and 0.04 percent of leaf content. Despite being present in far smaller quantities, 7-hydroxymitragynine plays a disproportionate role in kratom’s pharmacology, as you’ll see below.

How Mitragynine Works at Opioid Receptors

Mitragynine binds to the mu-opioid receptor, the same receptor targeted by morphine, codeine, and fentanyl. But it does not activate that receptor fully. In laboratory tests on human mu-opioid receptors, mitragynine behaved as a partial agonist, meaning it switched the receptor on only partway. Measured efficacy peaked at about 34 percent of the maximum signal a full agonist would produce.² Think of it like a dimmer switch turned to about a third of its range, rather than fully on.

What makes mitragynine especially interesting to pharmacologists is not just its partial activity but the kind of signal it sends inside the cell. When conventional opioids activate the mu receptor, they trigger two main signaling cascades. One involves a protein called G-protein, which produces pain relief. The other recruits a molecule called beta-arrestin, which is linked to side effects like constipation, sedation, and respiratory depression. Mitragynine strongly activates the G-protein pathway but produces no measurable beta-arrestin recruitment, even under conditions designed to enhance that signal.² Researchers describe this as G-protein-biased signaling, and it has been a major focus of opioid drug development for the past decade because, in theory, it could deliver pain relief with fewer dangerous side effects.

Why the Liver Changes the Story

Mitragynine does not simply circulate in your body unchanged. Your liver converts some of it into 7-hydroxymitragynine, a metabolite that is a much more potent opioid receptor agonist. This conversion is carried out by a family of liver enzymes called CYP3A, with CYP3A4 doing the heavy lifting in humans.³ A study in healthy volunteers confirmed that this metabolic conversion happens in people, not just in test tubes or rodents.⁴

This metabolic step complicates the picture considerably. When mice were given 7-hydroxymitragynine directly, it was roughly three times more potent at producing pain relief than mitragynine itself.⁵ Earlier research had found that when given by injection, 7-hydroxymitragynine was more potent than morphine in standard pain tests, and it remained active when given orally.⁶ However, the same mouse study that measured the potency difference also concluded that 7-hydroxymitragynine plays only a negligible role in mitragynine’s actual pain-relieving effects, because the amount formed through metabolism is so small.⁵ The debate about exactly how much 7-hydroxymitragynine contributes to the subjective experience of kratom in humans remains open.

Respiratory Depression and the Safety Question

The biggest danger of conventional opioids is respiratory depression: at high enough doses, they slow your breathing until it stops. This is what kills people in opioid overdoses. Because mitragynine activates opioid receptors, the obvious concern is whether it carries the same risk. A rodent study tested mitragynine at doses many times higher than what a human would typically consume and found no evidence of respiratory depression.⁷ The researchers attributed this to the same G-protein-biased signaling described above, since beta-arrestin recruitment is thought to drive the respiratory depressant effects of traditional opioids.

That said, kratom is not without toxicity risks. A case series of ten kratom poisoning patients found a variable mix of symptoms: most had altered consciousness, some showed elevated blood pressure and rapid heart rate, while others showed the opposite pattern with slow heart rate. Naloxone, the standard opioid overdose reversal drug, helped in some cases but not all. All ten patients survived, with symptoms resolving within two days.⁸ The inconsistent response to naloxone and the mixed sympathetic symptoms point to the fact that kratom’s effects are not purely opioid in nature, which brings us to the compound’s activity at other receptors.

Activity Beyond Opioid Receptors

Mitragynine does not exclusively target opioid receptors. It also interacts with alpha-2 adrenergic receptors, the same receptors targeted by clonidine and other blood pressure medications. This is one area where the science is genuinely unsettled. One research group found that mitragynine showed binding affinity at alpha-2 adrenergic receptors and behaved like an agonist in living rats, based on drug discrimination tests where clonidine and lofexidine produced similar effects.⁹ But even in that study, mitragynine failed to stimulate the receptor’s signaling in test-tube assays, leading the authors to suggest it was at best a low-efficacy agonist.

A more recent study from a related group arrived at a different conclusion entirely, finding that mitragynine actually acts as a competitive antagonist at alpha-2 adrenergic receptors, blocking them rather than activating them.¹⁰ The disagreement likely reflects the difference between what happens in isolated cells versus a living animal, where mitragynine’s metabolites and indirect effects can muddy the picture. Regardless of which interpretation wins out, this adrenergic activity helps explain why kratom overdose does not look like a classic opioid overdose. The mixed symptoms, where some patients present with high blood pressure and some with low, track with a compound that touches multiple receptor systems at once.

How Long Mitragynine Stays in Your System

Mitragynine reaches peak blood levels quickly, typically within about an hour of swallowing kratom.¹¹ But it leaves your body slowly. The elimination half-life, the time it takes for blood levels to drop by half, was about 23 hours in one study of nine subjects, though there was substantial variation between individuals.¹¹ A more recent study of repeated daily dosing found even longer half-lives, with the highest mean values reaching about 43 hours after a single dose and about 68 hours after multiple days of use.¹²

Those numbers have practical implications. A half-life of two to three days means that with daily use, mitragynine accumulates in your body over about a week before reaching a stable plateau. Steady-state concentrations were reached in about eight to nine days of daily dosing.¹² Almost none of the parent compound is excreted unchanged in urine, less than 0.2 percent, which means the body processes virtually all of it through metabolic pathways before elimination.¹¹ This heavy reliance on liver metabolism is what makes drug interactions a real concern.

Drug Interactions Worth Taking Seriously

Mitragynine is a strong inhibitor of CYP2D6, a liver enzyme responsible for breaking down a long list of common medications including many antidepressants, antipsychotics, beta-blockers, and some pain medications. Multiple studies have confirmed this, with mitragynine showing potent inhibition of CYP2D6 activity at low concentrations.¹³¹⁴ If you take kratom alongside a drug metabolized by CYP2D6, the drug could build up to higher-than-expected levels in your blood because mitragynine is competing for the same enzyme.

Mitragynine also inhibits CYP3A4, the same enzyme that converts it to 7-hydroxymitragynine. This creates a paradoxical situation: mitragynine depends on CYP3A4 for its own metabolism, but it also slows that enzyme down over time. One pharmacokinetic modeling study predicted that a two-gram dose of kratom could increase blood levels of midazolam, a common CYP3A4 test drug, by nearly six-fold, far exceeding the threshold for a clinically meaningful interaction.¹⁵ CYP3A4 metabolizes dozens of widely prescribed drugs, including certain statins, calcium channel blockers, and immunosuppressants. Anyone combining kratom with prescription medications should be aware that these interactions are not hypothetical; they have been predicted from real enzyme data at doses people actually take.

Dependence and Withdrawal

Regular kratom use can produce physical dependence. A survey of long-term users in Malaysia, where kratom has been consumed traditionally for generations, found that more than half of those who had been using it for six months or longer developed what the researchers classified as severe dependence. Another 45 percent fell into a moderate dependence category.¹⁶ The average daily mitragynine intake among these users was roughly 277 milligrams, spread across multiple servings of kratom drink.

Withdrawal symptoms resemble a milder version of opioid withdrawal. Physical symptoms commonly reported include muscle pain and spasms, difficulty sleeping, runny nose and watery eyes, hot flashes, fever, reduced appetite, and diarrhea. Psychological symptoms include restlessness, tension, anger, sadness, and nervousness.¹⁶ Users consuming three or more servings per day had higher odds of developing severe dependence and stronger cravings. In rodent experiments, withdrawal from 14 days of mitragynine treatment produced dose-dependent behavioral withdrawal signs that resembled morphine withdrawal, though the researchers also noted cognitive impairments in a memory task that are not typically associated with opioid withdrawal.¹⁷

The self-reported use of kratom as a substitute for conventional opioids is widespread. A systematic review found that multiple user surveys reported high self-rated success in using kratom to manage opioid withdrawal or reduce opioid use, with minimal self-reported side effects.¹⁸ The same review noted that some of these surveys were conducted with help from pro-kratom advocacy organizations, which is worth keeping in mind when evaluating the strength of that evidence.

Why Kratom Does Not Show Up on Standard Drug Tests

Standard urine drug screens test for common opioids, amphetamines, benzodiazepines, and a handful of other drug classes. Mitragynine is not included on any of these panels. Its chemical structure is an indole alkaloid, structurally unrelated to morphine or its derivatives, so it does not cross-react with typical opioid immunoassays. Detecting mitragynine requires specialized testing, typically liquid chromatography coupled with mass spectrometry, which can identify mitragynine in urine at extremely low concentrations, down to fractions of a nanogram per milliliter.¹⁹

Even specialized testing comes with complications. Kratom leaves contain several closely related alkaloids that are structural mirror images of mitragynine, called diastereomers. Standard analytical methods sometimes cannot separate mitragynine from these near-identical molecules, which means a positive result may actually reflect a mixture of compounds rather than a precise mitragynine measurement.²⁰ This matters in forensic and workplace settings where accuracy is legally consequential. The World Anti-Doping Agency placed mitragynine on its monitoring list in 2014 to track use in professional sports, though it has not been formally banned.²¹

Contamination in Commercial Products

Because kratom is sold as a dietary supplement or herbal product in most markets, it bypasses the kind of quality testing required for pharmaceuticals. The analysis of Chicago-area products mentioned earlier found more than just wild swings in mitragynine content. All but two of the tested samples contained detectable bacteria or fungi. Seven of the eight products also carried measurable levels of heavy metals including nickel, lead, and chromium.¹ None tested positive for salmonella, though salmonella contamination in kratom products had triggered a multistate outbreak and FDA warning several years earlier.

For a consumer, this means the mitragynine content listed on a label, if a label lists it at all, may not reflect what is actually in the product. And even if the mitragynine dose is roughly what you expect, the product could carry contaminants that introduce their own health risks. Some vendors have begun submitting to third-party testing through the American Kratom Association’s Good Manufacturing Practices program, but participation is voluntary and far from universal.

How Scientists Are Trying to Make Mitragynine Without the Tree

Kratom trees grow naturally in Southeast Asia, mainly in Thailand, Malaysia, and Indonesia, and they require tropical conditions that cannot be easily replicated in temperate climates. Harvesting depends on wild or semi-cultivated trees, which creates supply chain vulnerabilities and makes pharmaceutical-grade standardization difficult. Researchers have recently mapped out the biosynthetic pathway by which the kratom tree builds mitragynine from a precursor molecule called strictosidine, through a series of enzymatic steps.²² Using enzymes borrowed from other plant species and exploiting their ability to work on similar-but-not-identical substrates, scientists have achieved the first steps toward producing mitragynine in microbes like yeast or bacteria, bypassing the tree entirely.

This work is still early-stage and a long way from producing mitragynine at commercial scale. But the motivation is clear: if mitragynine or a modified version of it turns out to be a genuinely safer pain medication, having a synthetic or biosynthetic route would make clinical development far more practical than depending on tropical tree farms. The same G-protein-biased signaling profile that makes mitragynine unusual among opioid ligands is exactly what pharmaceutical companies have been trying to engineer into synthetic molecules for years, and here nature arrived at it independently.