Kratom (Mitragyna speciosa): The Plant, Its Alkaloids and What Research Shows About How It Works

Kratom_4U · October 14, 2026, 2:42pm

Reliable public information about kratom is hard to find. Most of what you read online is written by sellers or repeated from forum stories. This article explains the plant and its chemistry using published research, so you can understand what kratom is before you form an opinion about it.

This article does not give dosing guidance and does not recommend using kratom. Where the evidence is thin, it says so.

The plant

Kratom (Thai: กระท่อม) is the tree Mitragyna speciosa Korth. It is a tropical evergreen in the Rubiaceae, the coffee family. Being in this family explains two things about kratom.

First, kratom’s active compounds belong to a well-known chemical group called the indole alkaloids. Alkaloids are natural compounds made by many plants, and many of them act on the human body. Caffeine and nicotine are familiar examples. Indole alkaloids are a large subgroup that share the same ring-shaped chemical core. Second, in the field the tree grows like other Rubiaceae of the understorey, which is the shaded layer beneath taller forest trees.

Kratom grows wild across mainland and island Southeast Asia. Its range includes southern Thailand, peninsular Malaysia, Indonesia (especially Kalimantan, the Indonesian part of Borneo), the Philippines and New Guinea. It has also been reported from the Tanintharyi Region of southern Myanmar. In Thailand it is a plant of the deep South, where it was part of farming and village social life long before any law mentioned it.

The leaves are the part people use. Growers pick them from mature trees and dry them. The dried leaves are then used whole, ground to powder, or processed further into extracts.

Translator’s note: If you grow plants in Thailand or Southeast Asia and are thinking about kratom trees, this article covers the chemistry only. The field work is covered in Growing and Harvesting Kratom in a Tropical Climate. Read this article first so that you know which steps after harvest change what is in the leaf.

The alkaloids in the leaf

Kratom leaf contains dozens of alkaloids, but only a few matter for the plant’s effects:

Mitragynine: the main alkaloid in the leaf by weight. Most research on how kratom works is built around this compound.
Speciociliatine, speciogynine, paynantheine: close chemical relatives of mitragynine, present in meaningful amounts.
Corynoxine, corynantheidine, isocorynantheidine, mitraphylline: present in small amounts.
7-hydroxymitragynine (often shortened to 7-OH): the compound people talk about most, and the one they most often misunderstand.

When you read a product label or a claim about kratom, check which of these compounds it names. Mitragynine and 7-OH are not interchangeable, as the next section explains.

The key fact about 7-hydroxymitragynine: little or none in the living leaf

What a growing trial found

A research team led by Zhang published a controlled growing study in the journal PLOS One in 2022. The team grew kratom under three different light levels and then measured the alkaloids in the leaves. Mitragynine, paynantheine, corynoxine and the other alkaloids could all be measured, and all of them changed with the light treatment.

7-OH was below the limit of quantification in every sample. In other words, any 7-OH present was too little for the lab method to measure reliably.

The researchers took this as support for an existing view that the living plant makes little 7-OH. On that view, 7-OH forms after harvest. During drying, storage and processing, some mitragynine reacts with oxygen (oxidises) and turns into 7-OH.

This evidence has limits. It is one study of a single clone, meaning all the plants were cut from one parent and were genetically identical. The plants were grown for about three and a half months. The idea that 7-OH forms after harvest comes from earlier research and was not tested in this study. The finding is important, but it does not settle the question by itself.

The body also makes 7-OH

A team led by Kruegel tested this in the laboratory (ACS Central Science, 2019). They used liver preparations from mice and from humans, and both turned mitragynine into 7-OH. The conversion was done by CYP3A enzymes, a family of liver enzymes that break down many substances, including many medicines.

In mice, the 7-OH made in this way reached levels in the brain that the researchers judged high enough to explain most of mitragynine’s pain relief through the opioid receptors (explained in the next section). So a person who swallows leaf containing almost no 7-OH still ends up with some 7-OH, made by their own liver. Saying “the leaf is mitragynine, not 7-OH” is therefore too simple.

Why public discussion is so confused

The claim that “kratom is many times stronger than morphine” really describes 7-OH tested on its own. Dried leaf delivers mostly mitragynine, plus a little 7-OH that formed during drying. More 7-OH then forms slowly in the liver, and the speed of this differs from person to person.

A tablet sold as “kratom” but enriched with isolated 7-OH delivers a large amount of that compound directly. That exposure is very different from eating or drinking leaf.

Treat these as four different products, each giving a different amount of 7-OH: fresh leaf, dried leaf, standardised extract (an extract adjusted to contain a stated amount of an alkaloid), and 7-OH-enriched products. When you read any statement about “kratom”, check which of the four it means. If it doesn’t say, the statement tells you very little.

Translator’s note: Concentrated 7-OH products and their particular risks are covered in Kratom Risks: Drug Interactions, Concentrated 7-OH Products, Who Should Not Use It and What Is Still Unknown (Part 2 of 2).

How kratom acts on the body

A receptor is a protein on a cell. A substance attaches to it, like a key fitting a lock, and this changes what the cell does. The mu-opioid receptor is the main receptor that morphine and similar drugs act on to relieve pain. The following words come up often in this section:

Agonist: a substance that switches a receptor on.
Partial agonist: a substance that switches the receptor on only partly. Even in large amounts, it cannot produce the full response that a full agonist such as morphine produces.
Efficacy: how strongly a substance switches the receptor on once it has attached.
Potency: how little of a substance is needed to produce a set effect in a test.
Affinity: how tightly a substance attaches to the receptor.

Mitragynine

Mitragynine is a partial agonist at the mu-opioid receptor with fairly low efficacy. This explains, in terms of pharmacology, a common observation: at ordinary intakes, leaf preparations act quite differently from a conventional opioid drug.

7-OH: two different kinds of numbers

7-OH is also a mu-opioid partial agonist, but it is considerably more potent than mitragynine. The numbers repeated online come from different kinds of tests, so read them carefully:

Potency in animal tissue. A team led by Horie (Planta Medica, 2005) tested the compounds on guinea-pig ileum. This is a strip of guinea-pig small intestine kept alive in a lab bath, and it is a classic test of opioid strength. In this test, 7-OH was about 30 times more potent than mitragynine and about 17 times more potent than morphine. The widely repeated figures “13 times morphine, 46 times mitragynine” also come from guinea-pig ileum potency tests. None of these are receptor-affinity measurements, and none were measured in humans.
Receptor affinity. A team led by Váradi (Journal of Medicinal Chemistry, 2016) measured how well the compounds attached to a cloned mu-opioid receptor. A cloned receptor is made in lab-grown cells from its gene, so it can be tested on its own. 7-OH showed only moderate affinity, about 5 times higher than mitragynine.

Potency and affinity are different properties. Kratom writing often quotes one as if it were the other. When you see a “times stronger than morphine” figure, check what was measured, in what kind of tissue, and whether it was measured in humans.

Alpha-2 receptors

A team led by Obeng (Journal of Pharmacology and Experimental Therapeutics, 2022) studied a second mechanism in rats. Besides its mu-opioid effects, mitragynine also binds weakly to alpha-2 adrenergic receptors. 7-OH did not bind to them. These are a different group of receptors in the nervous system. Clonidine, a blood-pressure medicine, acts on the same receptors.

Simplified accounts of kratom often leave this out. If an explanation of kratom mentions only opioid receptors, you know it is incomplete.

“Biased signalling”: a hypothesis, not a safety result

After a receptor is switched on, it passes the signal into the cell along two main routes. One route uses G proteins. The other uses a protein called beta-arrestin. Opioid research has linked the beta-arrestin route to dangerously slowed breathing (respiratory depression) and severe constipation.

In 2016, a team led by Kruegel tested both mitragynine and 7-OH in lab-grown cells (Journal of the American Chemical Society). Both compounds switched on the G-protein route, but they recruited little or no beta-arrestin. This one-sided pattern is called “biased signalling”. It is the mechanism some people point to when they argue that kratom is less dangerous than a classical opioid.

That reading is disputed. A team led by Gillis (Science Signaling, 2020) studied other new “biased” opioid drugs. They argued that the apparent bias and milder side effects can be explained by low intrinsic efficacy. In other words, these drugs switch the receptor on only weakly, rather than steering the signal toward one route. Researchers still debate whether beta-arrestin causes opioid side effects at all.

This argument is often overstated. A signalling mechanism is a hypothesis about why harm might be lower. It does not show that harm is low. If someone offers “biased signalling” as proof that kratom is safe, treat it as an idea still being tested. What human harm data actually show is covered in Kratom Risks: What the Death Reports Show, Liver Injury, Dependence and Withdrawal (Part 1 of 2).

Effects change with the amount taken

The most-repeated fact about kratom is that its effects change with the amount taken. Low intakes feel stimulant-like. Higher intakes are sedating and relieve pain. This two-phase pattern is real and appears in the clinical literature. One source is StatPearls, a medical reference series published on the NCBI Bookshelf of the US National Library of Medicine.

Pharmacokinetics is the study of how the body absorbs, spreads, breaks down and removes a substance over time. The first human pharmacokinetic study of mitragynine was published by a team led by Trakulsrichai (Drug Design, Development and Therapy, 2015). The team studied ten regular kratom users in Thailand, and nine of them were included in the main analysis. Mitragynine blood levels rose in proportion to the dose.

The study reported a terminal half-life of about 23 hours (±16 hours). This is the time blood levels take to fall by half during the final, slow phase of removal from the body. The “±16 hours” shows how widely the results spread. Blood was sampled for only 24 hours, so later researchers consider this estimate imprecise. Mitragynine clearly does not act for only a short time, but its exact half-life in humans is not yet well established.

This article does not include a table of doses and effects. Such tables circulate widely online, but they come from users’ own reports, not from controlled studies. A table that looks precise when it isn’t is worse than no table at all. If you come across one, read it as a collection of user stories, not measured data.

What changes the alkaloid content of a leaf

This is where growing practice meets chemistry, and where some marketing claims fail.

Growing conditions

In the PLOS One study by Zhang’s team, plants grown under different light levels differed substantially in two ways: mitragynine concentration and total leaf yield. Two leaves from the same genetic line can therefore differ chemically, depending on where and how the tree grew.

Translator’s note: Suppose some of your trees grow in open sun and others grow shaded by taller trees. Keep the harvest from each spot separate and labelled. That way, if you ever have the leaf tested, you can see whether the spots differ. The study does not say which light level suits Thai conditions best. It only shows that light changes the chemistry.

Vein colour

Red-vein, green-vein and white-vein kratom are sold as separate products with different alkaloid profiles and different effects. Of all the marketing claims, this one has the weakest support. The literature search for this article found no controlled laboratory analysis showing that vein colour predicts alkaloid content once other factors are accounted for. Those factors are cultivar, leaf age, growing conditions and handling after harvest.

Growing conditions measurably shift alkaloid content, so the simplest explanation has not been ruled out. Vein colour may simply stand in for those other factors, or it may mean nothing at all. If a seller makes vein-colour claims, ask for the chromatogram. This is the printout from a lab test that shows which alkaloids are present and how much of each.

Handling after harvest

Earlier evidence suggests that much of the 7-OH in dried leaf forms after harvest. A 2025 study (described below) found that season and cultivar also matter. If 7-OH does form after harvest, then drying temperature, drying time, contact with air (oxygen) and storage conditions matter beyond quality control. They could change how much 7-OH the product contains before the body makes more of its own. Two batches of the same leaf, dried differently, are not the same product.

Translator’s note: Thai conditions add variables of their own. Examples are leaf dried at 30–35 °C, leaf dried in direct sun, and leaf that dries slowly in high rainy-season humidity. Each could end up with a different 7-OH content. One study has tested drying. A team led by Zhang (Frontiers in Plant Science, 2025) dried kratom leaf at temperatures from 25 to 80 °C, some of it after first leaving it to wilt. Leaf dried at 25 °C kept 3–26% more mitragynine than leaf dried at 60 °C. The 7-OH content did not change consistently with the drying treatment. It depended more on the season and the cultivar. Sun-drying and humidity were not tested, so there are still no data for these Thai conditions. Until such data exist, record these details for each batch:

the drying method
the temperature range
the number of drying days and the weather
how the leaf was stored, and for how long

If a lab test ever shows a difference between batches, your notes will help you find which step caused it.

Translator’s note on lab testing in Thailand: A lab test is the only way to know how much mitragynine and 7-OH a batch contains. Vein colour and appearance cannot tell you. Some Thai laboratories test for both compounds. For example, Central Laboratory (Thailand) Co., Ltd. has said it can test kratom for mitragynine and 7-OH. Its published information does not give a limit of quantification. Ask about other members’ experience in the community’s B2B Services: Laboratories, Logistics and Contract Work section. Start small: send two samples of the same leaf, each dried a different way. Before you send them, ask the lab which alkaloids it measures and what its limit of quantification is. If that limit is high, a result of “7-OH not detected” tells you little.

Kratom in Thailand

Thailand regulates kratom through a dedicated law, the Kratom Plant Act B.E. 2565 (2022). Among other things, the Act bans selling kratom leaf, or food that contains it, to people under 18 and to pregnant or breastfeeding women. Several neighbouring countries, including Malaysia and Indonesia, control or regulate kratom under other laws. Thailand is not the only country that regulates the plant.

Translator’s note: This article covers chemistry, not the full legal requirements. If you grow or sell kratom leaf, read the law topic linked above before you sell. At minimum, check the buyer’s age, and do not sell to pregnant or breastfeeding women.

Where the science is still unfinished

The evidence above has clear limits:

The research for this article found no published survey that compares the alkaloid content of Thai cultivars grown under identical, standardised conditions.
Peer-reviewed research has not clearly described how the age of a leaf at harvest changes its alkaloid profile.
Human pharmacokinetic data are thin, and published half-life estimates are imprecise. Almost all the data are for mitragynine, not for whole-leaf preparations.
How much 7-OH the human liver makes from mitragynine, and how much this varies between people, has not been well measured.
The contribution of the minor alkaloids to the overall effect is largely unknown.

Anyone who presents kratom pharmacology as settled, whether they say it is safe or dangerous, is going beyond the evidence.

Before you accept or repeat a kratom claim, check four things:

Which product does it refer to: fresh leaf, dried leaf, extract or a 7-OH-enriched product?
Which compound does it refer to?
What kind of measurement is it: potency, affinity or blood level?
Was it measured in humans?

If you have questions, or lab results from your own leaf, post them below this topic.

References

Zhang et al., “Plant growth and phytoactive alkaloid synthesis in kratom [Mitragyna speciosa (Korth.)] in response to varying radiance”, PLOS One 17(4): e0259326, 2022.
Kruegel et al., “7-Hydroxymitragynine Is an Active Metabolite of Mitragynine and a Key Mediator of Its Analgesic Effects”, ACS Central Science, 2019.
Kruegel et al., Journal of the American Chemical Society, 2016.
Horie et al., Planta Medica 71(3): 231–236, 2005.
Váradi et al., Journal of Medicinal Chemistry, 2016.
Gillis et al., “Low intrinsic efficacy for G protein activation can explain the improved side effect profiles of new opioid agonists”, Science Signaling, 2020.
Trakulsrichai et al., “Pharmacokinetics of mitragynine in man”, Drug Design, Development and Therapy 9: 2421–2429, 2015.
“Kratom”, StatPearls, NCBI Bookshelf.
Obeng et al., “Interactive Effects of µ-Opioid and Adrenergic-α2 Receptor Agonists in Rats: Pharmacological Investigation of the Primary Kratom Alkaloid Mitragynine and Its Metabolite 7-Hydroxymitragynine”, Journal of Pharmacology and Experimental Therapeutics, 2022.
Zhang et al., “Alkaloid biosynthesis in medicinal crop kratom (Mitragyna speciosa) varies with postharvest, genetic, and seasonal factors”, Frontiers in Plant Science, 2025.
Plants of the World Online (Royal Botanic Gardens, Kew), Mitragyna speciosa.
Transnational Institute, “Kratom in Myanmar and Southeast Asia”.