What is it?
Sedating alkaloid, not a focus enhancer
2L-THP is levo-tetrahydropalmatine, a tetrahydroprotoberberine isoquinoline alkaloid found in Corydalis and other plant sources. Older literature also calls it Rotundine. It blocks dopamine and other monoamine receptors, so it should not be treated as a benign cognitive herb.
Names, aliases and forms
Mechanisms of action
Dopamine blockade can cut against productivity
3L-THP antagonizes dopamine D1, D2, and D3 receptors and also affects adrenergic and serotonin receptors. That profile explains research interest in addiction and sedation, but it does not establish a nootropic benefit and raises caution around impairment and dopamine-active drugs.
Potential effects and evidence map
Human evidence is narrow but not limited to pharmacokinetics. A small randomized phase I study used 30 mg twice daily for 3.5 days in cocaine-using men and found no significant group difference in sleepiness, vital signs, ECG, laboratory measures, or reported side effects. An older randomized 120-person inpatient pilot after heroin detoxification used 60 mg twice daily for 4 weeks and reported withdrawal-related benefits, but the L-THP group had significantly higher early dropout and the study does not establish self-use. Analgesic, hypnotic, and cognitive claims otherwise rely mainly on preclinical or older medicinal literature.
Sedating pharmacology and older medicinal use do not establish a dependable relaxation benefit in healthy users.
Sleep-related findings come from an inpatient withdrawal study and animal models, not trials of primary insomnia or healthy-user sleep quality.
No controlled human evidence shows that L-THP improves focus or attention in healthy users.
Typical dosages and timing
One phase I study used 30 mg twice daily for 3.5 days. An older inpatient pilot used 60 mg twice daily for 4 weeks after heroin detoxification. These supervised, condition-specific regimens do not establish a typical supplement dose or self-treatment protocol.
Timing & effect horizon
In the small phase I study, oral L-THP reached median peak plasma concentration at about 1.5 hours and had a 13.3-hour The time for blood levels to fall by half during the final elimination phase.Source. These are pharmacokinetic measurements, not proof of when sedation starts or how long a desired effect lasts.
Safety, side effects and risk profile
L-THP has sedating pharmacology. A 3.5-day 30 mg twice-daily study did not significantly increase sleepiness, but THP-containing Jin Bu Huan overdose reports included marked CNS depression.
Dopamine-receptor antagonism makes combinations with antipsychotics or dopamine agonists clinically uncertain; additive impairment with alcohol or other sedating drugs is plausible but not well quantified in humans.
Human hepatitis cases were linked to a specific, variably composed or mislabeled Jin Bu Huan product containing L-THP. NIH LiverTox says the responsible ingredient and risk from isolated L-THP cannot be determined.
Pregnancy and breastfeeding safety for isolated L-THP has not been established in controlled human studies.
Purified levo-tetrahydropalmatine, racemic THP, Corydalis root, Stephania products, Rotundine medicines, and multi-ingredient blends are not interchangeable.
In a 2021 U.S. warning letter, FDA treated an anti-inflammatory claim for a marketed L-THP product as an unapproved-drug claim. That action was claim-specific and does not establish a universal ban or global status.
The short 30 mg twice-daily study did not find a significant sleepiness difference from placebo, but L-THP is pharmacologically sedating. Avoid driving or hazardous work until effects are known. Accidental ingestion of a THP-containing Jin Bu Huan product caused lethargy, ataxia, coma, and respiratory depression in children; product composition and dose were not comparable to controlled adult use.
NIH LiverTox documents more than a dozen liver-injury cases linked to a specific Jin Bu Huan product that contained L-THP but was variably composed or mislabeled. It cannot determine whether isolated L-THP, another ingredient, or contamination caused the injuries. That uncertainty supports caution, not a claim that purified L-THP is proven hepatotoxic.
Legal and regulatory status
In the United States, a 2021 FDA warning letter treated an anti-inflammatory claim for a marketed L-THP product as an unapproved-drug claim. This was a claim-specific enforcement action, not a blanket worldwide classification. Older literature describes medicinal use in China, but it does not establish current 2026 status in China, the EU, or any other market.
Practical buying and quality notes
- Look for levo-tetrahydropalmatine identity, amount per serving, plant source when relevant, and independent identity/contaminant testing. Corydalis blends, racemic THP, and purified L-THP should not be compared as though they were the same product.1
- Do not casually combine L-THP with alcohol, sleep medicines, other sedating substances, antipsychotics, or dopamine agonists. The interaction evidence is too limited to supply a dependable universal compatibility list.2
FAQ
Is L-THP a nootropic?
3Not by established human evidence. It is a pharmacologically active, sedating alkaloid studied mainly in addiction-related and preclinical contexts, with no controlled evidence of cognitive enhancement in healthy users.
Does this page recommend a dose?
4No. The page reports doses used in two supervised clinical studies so readers can interpret the evidence. Those regimens do not establish a typical supplement dose or a safe self-treatment protocol.
What do the timing numbers mean?
3The ~1.5-hour peak and ~13.3-hour half-life describe blood concentrations in one small phase I study. They are not validated onset or duration estimates for sleep, calm, pain relief, or any other desired effect.
References
- PubChem. L-Tetrahydropalmatine, CID 72301. Accessed 2026-06-30.
- l-tetrahydropalamatine: a potential new medication for the treatment of cocaine addiction. Future Medicinal Chemistry. 2012;4(2):177-186.
- Pharmacokinetics and Safety Assessment of l-Tetrahydropalmatine in Cocaine Users: A Randomized, Double-Blind, Placebo-Controlled Study. Journal of Clinical Pharmacology. 2017;57(2):151-160.
- Yang Z, et al. Medication of l-tetrahydropalmatine significantly ameliorates opiate craving and increases the abstinence rate in heroin users: a pilot study. Acta Pharmacologica Sinica. 2008;29(7):781-788.
- Dopamine D1 and D2 receptors mediate analgesic and hypnotic effects of l-tetrahydropalmatine in a mouse neuropathic pain model. Psychopharmacology. 2019;236(10):3161-3171.
- National Institute of Diabetes and Digestive and Kidney Diseases. LiverTox: Jin Bu Huan. Updated April 26, 2018.
- U.S. Food and Drug Administration. Warning Letter to Synaptent, LLC (MARCS-CMS 610683). November 9, 2021.