Pharmacology light: How the body processes plant compounds – explained using kratom as an example

Many terms around natural compounds sound complicated: “bioavailability,” “half-life,” “metabolites,” or “first-pass effect.” But the idea behind them is simple: How does a substance get into the body, what happens next, and how is it eliminated again? That’s what pharmacology (more precisely: pharmacokinetics) describes.

In this article, we explain the basics in a clear, general way—and use kratom (Mitragyna speciosa) as an example, because it is a natural product containing multiple alkaloids. Important: This is educational background information, not consumption advice.

Absorption: How do alkaloids enter the body?

When a substance is taken orally (by mouth), absorption typically works like this:

• Stomach & intestines: The substance is released in the digestive tract and then absorbed through the intestine.

• Solubility: Many alkaloids are more fat-soluble than water-soluble. That can influence how well they pass through the intestinal wall.

• Matrix (plant material): Kratom does not contain just one compound, but a mixture of different alkaloids. This “matrix” can influence absorption and the overall impression.

In short: With natural products, it’s not only “one substance” that matters, but also the surrounding composition in which it occurs.

Bioavailability: How much actually reaches the bloodstream?

Bioavailability means: What proportion actually reaches the bloodstream?
Some of it can be lost because:

• not everything is fully absorbed, or

• part of it is broken down early (e.g., in the liver).

For plant compounds such as kratom alkaloids, overviews often report ranges, because bioavailability can vary depending on the person, preparation, and sample.

First-pass effect: Why the liver matters

After absorption, blood from the intestine travels first to the liver. Many substances are already converted there—this is called the first-pass effect.

This helps explain why two people can reach different blood levels even with the same amount: liver enzymes do not work at the same speed or intensity for everyone.

Distribution in the body: Where does a substance “go”?

Once an alkaloid is in the blood, it distributes throughout the body. Key factors include:

• Fat solubility: Fat-soluble substances distribute differently than water-soluble ones.
• Protein binding: Many substances bind to proteins in the blood. Often, only the free fraction is directly available for interactions.
• Tissue permeability: Some areas are harder to reach (e.g., due to protective barriers in the body).

With natural products, multiple alkaloids may distribute in parallel—making the overall picture more complex than with single compounds.

Metabolism: What are metabolites?

When the body converts substances, metabolites are formed—breakdown or conversion products. This happens mainly in the liver, and partly in other tissues.

Important: Depending on the substance, metabolites can be

• less active,
• similarly active,
• or have their own distinct profile.

That’s why laboratory analyses sometimes look at the parent compound and specific metabolites, depending on the question.

Half-life: How long does a substance remain “measurable”?

The half-life is a rule-of-thumb number: How long does it take for the blood concentration to drop by about half?
It depends on factors such as:

• individual enzyme activity,
• dose and preparation,
• the sample composition (matrix),
• body weight, diet, and adaptation/tolerance.

That’s why scientific overviews typically report value ranges rather than a single number.

Elimination: How does a substance leave the body?

In the end, substances (or their metabolites) are eliminated—typically via:

• kidneys / urine, or
• bile / stool.

How quickly that happens depends on the substance itself and on individual metabolism.

Why people can respond differently

With natural products like kratom, people sometimes describe different impressions. From a pharmacological perspective, that is not surprising, because several factors can combine:

• Person: enzymes, metabolism, body composition
• Sample: origin, processing, alkaloid profile
• Preparation/matrix: form and composition
• Context: food, sleep, stress, adaptation/tolerance

That’s one reason why research prefers standardized samples and analytically measured contents.

Conclusion

“Pharmacology light” can be summarized like this:
A substance is absorbed, reaches the bloodstream with a certain bioavailability, is distributed in the body, metabolized in the liver (metabolites), has a certain half-life, and is finally eliminated.

Using kratom as an example highlights that natural products involve not only individual alkaloids, but also the matrix, origin, and individual factors. Understanding these basic terms makes it much easier to interpret claims in articles and studies.

Legal notice

This article is for informational purposes only and does not constitute medical or health advice. The content provided is not intended to encourage consumption. Each buyer is responsible for informing themselves about the applicable legal regulations.