What is it?
Sedating alkaloid, not a focus enhancer
2L-THP is levo-tetrahydropalmatine, an isoquinoline alkaloid found in Corydalis and other plant sources. Older literature also calls it Rotundine. It blocks dopamine and other monoamine receptors. A plant origin does not establish cognitive benefit or safety.
Human evidence is narrow and clinical
4The older 120-person inpatient pilot after heroin detoxification reported withdrawal-related outcomes but had substantially higher early dropout with L-THP. This selected population and attrition limit interpretation; the result does not establish healthy-user benefit.
A later clinical trial found no cognitive benefit
8A four-week randomized trial in 63 adults with schizophrenia on stable antipsychotic medication found no significant psychiatric or cognitive benefit. General tolerability was similar to placebo; two inflammatory markers increased, with uncertain clinical meaning. This patient study does not establish healthy-user efficacy or routine-use safety.
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 findings are limited and population-specific. A small randomized phase I study in cocaine-using men found no significant group difference in sleepiness, vital signs, ECG, laboratory measures, or reported side effects. An older inpatient pilot after heroin detoxification reported withdrawal-related outcomes but had substantially higher early dropout with L-THP. A later four-week randomized study in 63 adults with schizophrenia found no significant psychiatric or cognitive benefit; overall tolerability was similar to placebo. None establishes cognitive enhancement or sleep efficacy in generally healthy users.
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
The phase I safety study used the lower dose for 3.5 days; the older inpatient pilot used the higher dose for 4 weeks after heroin detoxification. These are separate, supervised regimens in specific populations, not a typical supplement dose. Study windows do not establish a recommended cycle.
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
Sedating pharmacology warrants impairment caution. The short phase I trial found no significant sleepiness difference from placebo. Large accidental ingestions of L-THP-containing Jin Bu Huan tablets caused severe CNS and respiratory depression in children; this does not estimate ordinary adult-use risk.
Interactions are incompletely characterized. One small four-week trial alongside stable antipsychotic medication found similar general tolerability to placebo; this does not establish compatibility across dopamine-active medicines. Additive impairment with alcohol or sedatives remains a pharmacological concern.
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.
A 2021 U.S. FDA warning letter cited an anti-inflammatory claim for a marketed L-THP product among unapproved-drug claims. The historical action was product/claim-specific and does not establish a universal ban or current international status.
The short phase I study found no significant sleepiness difference from placebo, but its selected population and brief exposure cannot establish ordinary-use safety in generally healthy adults. A typical supplement dose and longer-term risk are not established, so the overall risk is unscored. This does not mean safe: sedating pharmacology warrants impairment caution, and the separate poisoning and liver reports below remain relevant.
CDC documented three young children with central nervous system depression, including breathing impairment and marked slowing of the heart rate, after large accidental ingestions of Jin Bu Huan tablets. The tested tablets contained L-THP without detected pharmaceutical contamination. All recovered, but these poisonings demonstrate a severe overdose hazard rather than the frequency of harm at ordinary adult doses.
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.
Interactions and cautions
A small four-week trial in adults on stable antipsychotic medication found no excess general side effects, but it cannot establish safety across dopamine-active combinations. Additive impairment with alcohol, sleep medicines, or other sedating substances remains a pharmacological concern rather than a quantified human interaction risk.
Legal and regulatory status
In the United States, a 2021 FDA warning letter cited an anti-inflammatory claim for a marketed L-THP product among unapproved-drug claims. This historical action concerned that product and its claims; it does not establish current worldwide ingredient legality. Older literature describes medicinal use in China, but current classification, sale, and import rules require market-specific verification.
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
- Compare listed prices per declared amount of purified L-THP, with matching formulation and serving basis. A Corydalis extract weight is not an L-THP amount unless the label quantifies this constituent; an extract ratio alone cannot supply the conversion. Check bottle servings and shipping separately before comparing total cost.2
FAQ
Is L-THP a nootropic?
8Human evidence does not establish cognitive enhancement in healthy users. A small four-week randomized study in adults with schizophrenia found no significant cognitive or psychiatric benefit. Those clinical findings cannot validate consumer focus or memory claims.
Is a consumer dose established?
4No typical supplement dose is established by the cited clinical studies. They used supervised regimens in selected patient groups and do not establish a safe self-use 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.
- Kelly DL, et al. L-Tetrahydropalmatine, a Novel Dopamine Antagonist, Fails to Improve Psychiatric Symptoms as Adjunctive Treatment for Schizophrenia. Schizophrenia Bulletin Open. 2020;1(1):sgaa026.
- Centers for Disease Control and Prevention. Jin Bu Huan Toxicity in Children — Colorado, 1993. MMWR. 1993;42(33):633-636.