Skullcap

Scutellaria lateriflora L. was named by Linnaeus in 1753 and is the accepted name in Kew’s Plants of the World Online (POWO), which places it in the mint family, Lamiaceae, and describes it as a perennial of temperate regions. Its native range covers most of North America: in Canada from British Columbia, Manitoba, Ontario, and Québec to New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland, and in the United States from Washington, Oregon, California, and Arizona east to New England, Florida, and Texas. Wang and colleagues (Pharmaceutical Biology 2018) put the genus Scutellaria at around 360 species. Chinese skullcap, Scutellaria baicalensis Georgi, was named in 1775 and is native, according to POWO, to Siberia (Irkutsk, Buryatiya, Chita, and Yakutiya), the Russian Far East, Mongolia, Inner Mongolia, Manchuria, north-central and south-central China, Korea, and Vietnam, with an introduced population in Germany. Older books call it Scutellaria lanceolaria or S. macrantha, names POWO now treats as synonyms.

King’s American Dispensatory (1898) describes American skullcap as a smooth, much-branched herb 1 to 2 feet tall, with a slender four-angled stem, growing in damp places on stream banks, in meadows and ditches, and beside ponds. The opposite leaves are ovate, 1 to 2 inches long, with toothed edges and stalks about an inch long. In July and August small pale-blue flowers, about a quarter of an inch long, open in slender one-sided sprays (racemes) from the leaf axils, which is what lateriflora, “side-flowering,” refers to. The calyx carries a helmet-shaped appendage on its upper lip, and the fruit is four small nutlets. King’s complained that much of the skullcap sold in its day came from S. versicolor and S. canescens, sturdier plants 2 to 4 feet tall with inch-long flowers in a single terminal spray. Chinese skullcap looks different: Zhao and colleagues (Journal of Pharmacy and Pharmacology 2019) describe a thick, fleshy rhizome up to 2 cm across, stems 30 to 120 cm tall, narrow leaves 1.5 to 4.5 cm long, and terminal racemes of purple, purple-red, or blue flowers 2.3 to 3 cm long.

For American skullcap the medicine is the aerial parts, the mature leaves and flowering tops gathered in flower, and Health Canada’s monograph covers the dried herb top. For Chinese skullcap it is the root, Scutellariae Radix. Both are dominated by flavones. Gafner and colleagues (Journal of AOAC International 2003) found an ethanol extract of S. lateriflora to be characterized mainly by baicalin, lateriflorin, dihydrobaicalin, and baicalein, and Awad and colleagues (Phytomedicine 2003) measured baicalin at 40 mg per gram in one extract, along with small amounts of the calming brain messenger GABA. Zhang and colleagues (Phytomedicine 2009) isolated 12 phenolic compounds, 10 of them flavonoids, and found that commercial products contained similar compounds in widely varying amounts. Baicalin is baicalein bound to glucuronic acid, and wogonin is a close relative. Wang and colleagues list 126 small molecules and 6 polysaccharides from S. baicalensis, mostly from the root, which the Chinese Pharmacopoeia requires to contain at least 9% baicalin. Lin and colleagues (Phytochemical Analysis 2009) note that skullcap’s diterpenes lack the furan ring that makes germander’s diterpenes toxic to the liver.

LiverTox records that American skullcap was used for centuries by Native Americans for menstrual disorders, nervousness, and digestive and kidney problems. Its most famous early claim was against rabies. Among its old names King’s American Dispensatory lists mad-dog weed and madweed, and Health Canada still recognizes mad-dog skullcap as a common name. In June 1820 the London Medical and Physical Journal printed two reports, by Stillwell and by Fiske, each headed “Case of Hydrophobia, Successfully Treated by the Scutellaria Lateriflora.” Skeptics followed. King’s called its use in hydrophobia “still a matter of uncertainty,” Finley Ellingwood’s American Materia Medica (1919) judged the herb “doubtless too feeble for such a purpose,” and Felter’s Eclectic Materia Medica (1922) traced its “great reputation” to reports by New Jersey physicians, a claim time had totally failed to sustain. No modern study has tested skullcap against rabies, and any bite from an animal that might carry rabies needs urgent medical care.

The Eclectics, nineteenth-century American physicians who favored native plants, made skullcap a staple nervine. King’s called it tonic, nervine, and antispasmodic, recommending it for chorea (involuntary jerking movements), convulsions, tremors, neuralgia, restlessness and wakefulness after illness or overwork, and teething children, and said that in delirium tremens an infusion drunk freely “will soon produce a calm sleep.” It added that the dried herb loses its properties with age, “hence the many failures in therapy.” Felter was more measured: useful for insomnia from worry or nervous irritability and for chorea combined with black cohosh and valerian, but not for epilepsy or Parkinson’s disease. Ellingwood called it “not a remedy of great power.” Mainstream pharmacy was harsher. The 1918 Dispensatory of the United States, noting that skullcap had moved from the US Pharmacopoeia to the National Formulary, called it “as destitute of medicinal properties as a plant may well be.”

Chinese skullcap has a far longer written history. Wang and colleagues record that huang qin was first described in Shennong’s Classic of Materia Medica around 200 AD, that huang means yellow and qin an herb to stop bleeding, and that Chinese medicine credits it with clearing heat, drying dampness, purging fire, detoxifying, stopping bleeding, and preventing miscarriage. It is listed in the Chinese, European, and British pharmacopoeias, and Zhao and colleagues count more than 180 Chinese Pharmacopoeia prescriptions that contain it, including formulas for diarrhea, sore throat, and jaundice. In China baicalin itself has been developed into tablets for hepatitis. In Japan the root, called ougon, is an ingredient of Kampo formulas such as sho-saiko-to. King’s noted that Takahashi had isolated a crystalline compound from the root of the Japanese plant in 1889. In the West, Chinese skullcap reached pharmacies mainly through joint products, notably Limbrel, sold as a prescription “medical food” from 2004 until its 2017 recall.

The leading idea is that skullcap’s flavones act on the GABA-A receptor, the brain’s main calming switch and the target of benzodiazepine drugs such as diazepam. In laboratory binding tests, Hui and colleagues (Planta Medica 2000) found four flavones from Chinese skullcap root that bind the receptor’s benzodiazepine site: wogonin most strongly, then baicalein, scutellarein, and, much more weakly, baicalin. In a follow-up study (Biochemical Pharmacology 2002), wogonin enhanced GABA-activated currents in nerve cells, and oral doses of 7.5 to 30 mg per kg calmed mice in standard anxiety tests without sedating them or relaxing their muscles; a benzodiazepine-blocking drug abolished the effect. These are cell and mouse findings using a single purified compound, which is not what a skullcap capsule delivers. LiverTox summarizes the common view that skullcap flavonoids may act like weak benzodiazepines, but this has not been shown in people.

For American skullcap itself, the evidence is from animals. Awad and colleagues gave rats oral extracts of S. lateriflora and saw anxiety-reducing behavior in two standard tests, the open field and the elevated plus-maze, and they suggested that baicalin, baicalein, and the small amount of GABA in the herb might contribute. Zhang and colleagues found anticonvulsant activity in rat models of acute seizures, which fits the Eclectic use for convulsions but has never been tested in people with epilepsy. Lab work on Chinese skullcap is vast: Wang and colleagues summarize antiviral, antibacterial, anti-inflammatory, antioxidant, liver-protective, nerve-protective, and anticancer activity in cells and animals. MSKCC notes that most of this research is preclinical and that baicalin can have opposite effects on blood vessel growth at low and high doses. Laboratory activity of this kind is common among flavonoids and is not evidence of benefit in humans.

Human data on what happens to these compounds in the body come mostly from Chinese skullcap flavones. In a phase I study by Li and colleagues (Journal of Ethnopharmacology 2014), single doses of 100 to 2,800 mg of baicalein were well tolerated by 72 healthy adults; less than 1% appeared in urine and about 27% passed out unchanged in feces. Baicalin is absorbed well enough to matter for drugs: in healthy volunteers it lowered blood levels of rosuvastatin and sped up the breakdown of bupropion, as the interactions section explains. No study has shown a measurable brain effect of skullcap flavones at supplement doses. How skullcap products injure the liver is unknown, according to LiverTox. For germander, the adulterant, the mechanism is clearer: LiverTox explains that its furan-containing diterpenes are converted by liver enzymes into reactive compounds that damage liver cells.

Anxiety is the main modern use, and the trials are few and weak. Wolfson and Hoffmann (Alternative Therapies in Health and Medicine 2003), whose lead author was listed at Phytos Inc. in California, reported “noteworthy anxiolytic effects” in a double-blind, placebo-controlled study of healthy volunteers. Sarris and colleagues (Evidence-Based Complementary and Alternative Medicine 2012) described it as one small study of single doses whose methodology was weak and whose results were poorly reported, and Lin and colleagues noted that it used a non-validated scale. Brock and colleagues (Phytotherapy Research 2014) then ran a better-designed randomized, double-blind crossover trial in 43 healthy adults, giving 350 mg of S. lateriflora three times a day or placebo for two weeks each. Anxiety scores did not differ from placebo (p = 0.191), although 81% of participants were only mildly anxious or less and baseline anxiety differed between groups. Total mood disturbance fell significantly from the start of the skullcap period, but not the placebo period, without loss of energy or concentration. Verdict: no trial in people with an anxiety disorder; benefit is unproven.

Sleep now has one encouraging trial. Di Minno and colleagues (Nutrients 2025) randomized 66 adults aged 18 to 70 with mild to moderate primary insomnia, at a single Italian center, to a capsule of 400 mg a day of S. lateriflora extract standardized to 10% baicalin or placebo for 56 days each, separated by a 28-day washout. On the Pittsburgh Sleep Quality Index (PSQI), where lower is better, scores fell from 13.0 to 9.5 during the skullcap period and rose from 11.5 to 13.3 during the placebo period, and sleep diaries showed shorter time to fall asleep and longer sleep. No side effects were reported. The paper states that the research received no external funding; the extract was supplied by an Italian company, EPO. The authors acknowledge that all outcomes were self-rated and that a carryover effect suggests the washout was too short. Health Canada accepts skullcap as a traditional remedy for restlessness and nervousness that helps promote sleep. Verdict: promising but unconfirmed; an independent trial with objective sleep measures is needed.

Mood and stress studies have mostly used Chinese skullcap, often in blends. Dormal and colleagues (Nutrients 2025) randomized 180 adults with mild to moderate depressive symptoms to 20 mg a day of a S. baicalensis extract standardized to 90% baicalin, a saffron extract, both, or placebo for six weeks. Depression scores on the main outcome, the Beck Depression Inventory, fell in every group, and the fall did not differ between groups; a well-being score improved more with skullcap than placebo in the second half of the trial. The study was funded by Comercial Química Massó, the ingredient supplier, which helped design it and write the paper. Dodd and colleagues (Journal of Psychopharmacology 2025) tested a tablet combining Chinese skullcap, hawthorn, magnesium, and chromium in 43 stressed adults, 35 analyzed, over 15 days and reported better mood and anxiety scores; the sponsor, A. Vogel, employed one author. Neither study shows what skullcap adds on its own. Verdict: no reliable evidence for low mood.

Chinese skullcap is mostly used inside formulas. MSKCC notes that it has not been studied in clinical trials as a single agent for cancer, only within formulas such as PC-SPES and sho-saiko-to, and that human studies are limited overall. In a small Korean crossover trial by Shin and colleagues (American Journal of Physiology, Endocrinology and Metabolism 2020), 3.52 g a day of S. baicalensis added to metformin for eight weeks improved glucose tolerance in type 2 diabetes, but some participants developed raised liver enzymes. For osteoarthritis, a one-week trial by Arjmandi and colleagues (Journal of Medical Food 2014) compared 500 mg a day of UP446, a blend of Chinese skullcap and black catechu (Acacia catechu), with the painkiller naproxen in 79 adults and reported less pain, but there was no placebo group. Products of the same type, Limbrel and Move Free Advanced, have been linked to liver injury. Verdict: the root is an important ingredient of traditional formulas, but no single-herb use is established.

Other traditional uses rest on history rather than trials. Health Canada accepts American skullcap as a traditional remedy for menstrual pain, based on herbal texts rather than studies. The Eclectics used it for chorea, tremors, and convulsions, and it does have anticonvulsant activity in rats, but no human trial has tested it in epilepsy, and Felter himself thought it useless there. Chinese medicine uses huang qin for fevers, diarrhea, sore throat, and hepatitis, and MSKCC lists hepatitis, arthritis, and cancer among its purported uses, none supported by good trials of the herb alone. Anyone looking for a calming herb with more research behind it will find stronger evidence on the passionflower, valerian, and lemon balm pages, and seizures, anxiety disorders, persistent insomnia, and depression all deserve medical care rather than a herbal experiment.

American skullcap is sold as dried herb for tea, tinctures and fluid extracts, and capsules of powdered herb or dried extract, often blended with valerian, passionflower, or other calming herbs. Health Canada’s monograph, updated in 2024, allows adults 18 and older 0.25 to 12 g of dried herb top a day as powder or alcohol-based extracts, or 3 to 12 g a day as water-based preparations such as an infusion or decoction, with no set duration. The trials used much smaller amounts of concentrated extract: 350 mg three times a day in the Brock trial and 400 mg once a day of an extract standardized to 10% baicalin in the 2025 insomnia trial. Historical doses were similar to Health Canada’s: King’s made “a very strong infusion” from half an ounce of recently dried herb in half a pint of boiling water, and the 1918 Dispensatory gave 2.0 to 5.8 g. Doses from one product cannot be assumed to match another, because the ratio of herb to extract and the flavonoid content vary.

Chinese skullcap root is used mainly as one ingredient of decocted formulas or patent pills, granules, and capsules prescribed in Chinese medicine, and the Chinese Pharmacopoeia requires the dried root to contain at least 9% baicalin. Western supplements usually contain root extracts standardized to baicalin, sometimes almost pure: the 2025 mood trial used 20 mg of an extract that was 90% baicalin. Joint products have paired Chinese skullcap with black catechu, the combination behind flavocoxid (Limbrel), which was sold as 250 mg and 500 mg capsules, and UP446, studied at 500 mg a day. Because the root and the aerial parts of the two species differ in chemistry and safety record, a product label that just says “skullcap” is not enough. Look for the full Latin name, the plant part (American skullcap herb or Chinese skullcap root), and, for extracts, the baicalin content.

Quality has been a problem for well over a century. King’s warned in 1898 that much skullcap on the market was really other Scutellaria species, and that the dried herb loses potency with age. More seriously, Lin and colleagues report that American skullcap has occasionally been adulterated with germander, Teucrium canadense or T. chamaedrys, which contains liver-toxic diterpenes, and LiverTox notes that germander or mislabeling was found in some suspected skullcap liver cases. Analytical methods can now tell them apart: Gafner and colleagues used chromatography and microscopy, and Lin and colleagues could detect as little as 1% Teucrium mixed into skullcap. Zhang and colleagues found the same compounds in different commercial skullcap products but in widely varying amounts. Practical points: choose single-herb products that name Scutellaria lateriflora aerial parts, prefer brands that test identity against germander, and be wary of multi-herb “sleep” or “stress” blends that make it impossible to know what you are taking.