Uncaria (Gou Teng)

• May lower blood pressure further when taken with blood pressure medicine. Gou teng alkaloids relax artery muscle by blocking calcium channels in lab work, and a review of animal studies lists lowered blood pressure, a slower heart rate and sedation. In trials of multi-herb formulas added to blood pressure drugs, pressure fell more than with the drug alone. That is the aim in a trial, but outside one it can mean dizziness or fainting. No report of harm from the herb alone was found; it is a reason to tell your prescriber, not a proven danger. Laboratory research ^{7 12 8 14}
• Yokukansan contains liquorice: low potassium and high blood pressure (pseudoaldosteronism). Yokukansan is a seven-herb formula that includes Uncaria hooks and liquorice. In a hospital cohort of 389 people, 94 (24.2%) developed low potassium, a median of 34 days after starting. Risk rose with other potassium-lowering drugs, low blood albumin and full-dose use. A Japanese reporting database found a higher rate of pseudoaldosteronism (high blood pressure, low potassium, muscle weakness) with Yokukansan than with other liquorice formulas, with older age, dementia and body weight under 50 kg as risk factors. The authors say it can lead to death. The cause is the liquorice, not Uncaria, so this applies to Yokukansan and similar liquorice formulas, not to gou teng alone. Cohort study ^{13 6 19}
• Do not mix it up with cat's claw (Uncaria tomentosa). Gou teng is a different plant from the South American cat's claw. A 2026 case report describes a woman who tried to stop a high-dose cat's claw supplement and developed severe delirium and a dangerously slow heartbeat that needed a pacemaker. One case cannot show cause and it concerns another species, but it shows why the exact plant matters. Case report ^{5 9}
• Human safety data for gou teng alone are very thin. A 2026 review says adverse effects in people are rare (nausea, diarrhoea; kidney effects and nerve problems are extrapolated from cat's claw) and that long-term safety is not studied. Sleepiness was reported once in a 4-week trial of a formula. No regulator monograph was found. Review ^{9 17 23}
• Quality differs by species and region. The Chinese Pharmacopoeia allows five Uncaria species, which differ chemically. In a 2025 study of 50 samples, only U. rhynchophylla could be bought on the herbal market; the others came from the wild. Alkaloid content varies, and long boiling can destroy heat-sensitive alkaloids. Products and trials may not be comparable. Laboratory analysis ^{3 9}

No LiverTox entry for gou teng was found. A 2022 paper says liver toxicity of the herb 'has been reported repeatedly in recent years', but the underlying human case reports were not identified or read, and its own analysis was a computer prediction (cadambine, rhynchophylline, corynoxeine, isocorynoxeine, strictosamide and mitraphylline flagged as possible). The 2026 review says hirsutine is converted by CYP3A4 into reactive products that could harm the liver at high dose or long use, but a clinical link is not shown. In the formula add-on meta-analysis no liver dysfunction occurred. Treat liver safety as not established. ^{18 9 8 23}

How often. No frequency of liver injury is available.

Monitoring. No monitoring advice was found. Stop and seek care for yellow skin or eyes, dark urine, pale stools or severe tiredness.

This is a safety connection. It is not evidence that Uncaria (Gou Teng) supports liver health.

Summary. No human poisoning with gou teng alone was found in the sources read. Animal tests found no acute toxicity.

Animal. A 2026 review (citing earlier work) reports an oral LD50 for rhynchophylline above 5 g/kg in mice with no acute toxicity, and no organ changes in a 90-day rat study. Rodent data may overstate human safety.

Human doses studied. Trials used multi-herb formulas. Ask a doctor or pharmacist about amounts.

High dose or long term signals. The review flags possible liver injury at high dose or long use through a reactive hirsutine metabolite and says long-term safety is understudied.

Overdose response. Dizziness or sedation (review, from traditional and animal data). Seek medical care for fainting or a very slow pulse.

Genotoxicity. Not found.

Toxic plant parts. The hooked stem is the used part. Other parts were not covered by the sources read, and no toxic part was identified.

The main concern is knowing which species is in a product and how much active alkaloid it holds.

Five legal source species. The Chinese Pharmacopoeia accepts five Uncaria species with different alkaloid profiles. Only U. rhynchophylla was available on the herbal market in a 50-sample study; the other four were wild-collected. ³

Alkaloid loss with cooking. Heat-sensitive alkaloids degrade with long boiling, which is why the hooks are traditionally added late. ⁹

Look-alike confusion. Cat's claw (Uncaria tomentosa) is a different plant with its own safety record. ⁵

• Fainting, severe dizziness or a very slow pulse: seek urgent care.
• Muscle weakness or cramps, palpitations, new swelling or sharply higher blood pressure while taking Yokukansan or another liquorice formula: seek medical care promptly (possible low potassium).
• Yellow skin or eyes, dark urine or severe tiredness: stop and seek care (possible liver injury).
• Severe confusion or agitation after using or stopping any Uncaria supplement: seek urgent care.

Stop the supplement and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.