Reviewed August 2026 by the Corydalis Labs Technical Team. How we research and review.
The short answer
THP is an isoquinoline alkaloid found in several plant species, most notably Corydalis yanhusuo. It has been characterised in the scientific literature for decades, appears in traditional herbal preparations across eastern Asia, and is available from botanical suppliers as an isolated compound.
The name is descriptive: it is the tetrahydro form of palmatine, another alkaloid from the same family. You will also see it written as l-tetrahydropalmatine, l-THP, or rotundine — these refer to the levorotatory form, which is the one that occurs in the plant and the one that carries most of the documented activity.
What kind of molecule it is
THP belongs to the isoquinoline alkaloids. This matters more than it might sound, because the compound most people arrive here comparing it to — mitragynine, from the kratom leaf — is an indole alkaloid. Those are two structurally distinct families with different cores, different biosynthetic origins, and different pharmacology.
Put plainly: THP and mitragynine are not variations on a theme. They are unrelated compounds from unrelated plants that happen to be discussed in the same commercial category because of how the market evolved. The comparison page sets out the differences.
Common confusion worth clearing up
THP is sometimes written "THC" by autocorrect or misheard on a call. They have nothing to do with each other. THC is a cannabinoid from Cannabis sativa; THP is an isoquinoline alkaloid from a poppy-family plant. Different molecules, different plants, different regulatory positions entirely.
How it is understood to work
The published literature on THP associates its activity primarily with dopaminergic signalling — it is described as a dopamine receptor antagonist — rather than with opioid receptors. This is the clearest pharmacological line between THP and the kratom alkaloids, which are discussed in the literature in terms of opioid receptor activity.
We state this carefully because the honest position is that the research on THP is more developed than the research on its 13-OH derivative. What is documented about the parent compound should not be assumed to transfer wholesale to the derivative, and we would rather flag that than let an implication stand. What we can say about 13-OH specifically is here.
THP versus 13-OH
| THP | 13-OH | |
|---|---|---|
| Relationship | Parent alkaloid | Hydroxylated derivative |
| Source | Corydalis yanhusuo | Derived from the same plant material |
| HPLC retention | 15.0 minutes | 18.8 minutes |
| Literature | Decades of published work | Far less published work; most knowledge is practitioner-level |
| In a blend | Contributes, but less per milligram | Contributes more per milligram at the same inclusion |
| Scheduled? | No | No |
Because THP is cheaper and more widely available, material sold as 13-OH that is actually THP is a real risk in this market. The two separate cleanly under HPLC, so the test is straightforward — but only if someone runs it. How we verify identity.
Where THP shows up commercially
THP is sold as an isolated compound by botanical and research suppliers, appears in traditional Corydalis preparations, and shows up as a declared ingredient in some finished botanical products. It is not a controlled substance in the United States.
We supply the derivative rather than the parent, because the derivative performs better in the blends our customers build. THP itself is a legitimate ingredient with its own history — it simply requires more of it to achieve what a smaller inclusion of 13-OH achieves. Inclusion guidance is here.
Common questions
Tetrahydropalmatine does not appear on the federal controlled substance schedules or the DEA List I/II chemical lists as of August 2026. As always, verify current status with your own counsel before commercialising anything — and note that a compound being unscheduled federally does not settle every question about how a finished product may be marketed. The regulatory summary covers this.
Effectively, in commercial usage. "l-THP" specifies the levorotatory enantiomer, which is the form that occurs in the plant. Material described simply as THP is generally this form. Rotundine is another name for the same compound.
No. 13-OH is a hydroxylated derivative — a different molecule with a hydroxyl group added at the 13 position. They separate cleanly by HPLC, at 15.0 and 18.8 minutes respectively, which is how a lab tells them apart.
No. THP comes from Corydalis yanhusuo, a plant in the poppy family. Kratom is Mitragyna speciosa, in the coffee family. The two plants are unrelated and so are their alkaloids.