Yerba Santa

Yerba santa was used by many California peoples, including the Atsugewi, Costanoan, Kawaiisu, Miwok, Pomo, Yokut, Yuki and Yurok ^{5Reference 5Maher P et al. · 2020In vitroThe Value of Herbarium Collections to the Discovery of Novel Treatments for Alzheimer’s Disease, a Case Made With the Genus Eriodictyon — in vitroView study →}. They used it for colds, for respiratory infections including whooping cough, pneumonia and tuberculosis, for asthma and rheumatism, and on sores ^{1Reference 1Satyal P et al. · 2026Chemical Composition of Eriodictyon californicum (California Yerba Santa) Cultivated in Ontario, Oregon, USA — analytical/phytochemistryView study →}. Other recorded uses include headaches and inflammation ^{5Reference 5Maher P et al. · 2020In vitroThe Value of Herbarium Collections to the Discovery of Novel Treatments for Alzheimer’s Disease, a Case Made With the Genus Eriodictyon — in vitroView study →}.

The Atsugewi chewed the plant for coughs and colds and used the leaves and branches in a steam bath for rheumatism. The Miwok drank an infusion of the leaves and flowers for coughs and colds, and applied a leaf poultice to aching or sore spots ^{1Reference 1Satyal P et al. · 2026Chemical Composition of Eriodictyon californicum (California Yerba Santa) Cultivated in Ontario, Oregon, USA — analytical/phytochemistryView study →}.

Early settlers adopted the leaf extract as a remedy for coughs, colds, influenza (“grippe”) and asthma ^{21Reference 21Howard · 1992Eriodictyon californicum, California yerba santaView study →}.

Yerba santa products were also used for many years in pharmacy to mask the bitter taste of other medicines ^{16Reference 16Ley JP et al. · 2005In vitroEvaluation of bitter masking flavanones from Herba Santa (Eriodictyon californicum) — sensory / in vitroView study →}.

A Salk Institute group built a set of screening assays that model several age-related causes of nerve-cell death at once. Screening a large library of medicinal-plant extracts, they identified the E. californicum flavanone sterubin as the active neuroprotective component ^{2Reference 2Fischer W et al. · 2019In vitroOld age-associated phenotypic screening for Alzheimer’s disease drug candidates identifies sterubin as a potent neuroprotective compound from Yerba santa — in vitro screeningView study →}.

Follow-up work showed that sterubin protects nerve cells against several distinct causes of cell death and strongly induces Nrf2. Of seven closely related flavonoids tested, only sterubin combined strong neuroprotection with strong anti-inflammatory activity ^{3Reference 3Liang Z et al. · 2022In vitroStructural Requirements for the Neuroprotective and Anti-Inflammatory Activities of the Flavanone Sterubin — in vitroView study →}.

The plant makes only the (S)-form of sterubin. Both forms protected nerve cells equally in vitro, and low oral doses preserved short- and long-term memory in a mouse model of Alzheimer’s disease ^{6Reference 6Hofmann J et al. · 2020In vitroSterubin: Enantioresolution, Configurational Stability, Enantiomeric Purity in Nature, and Neuroprotective Activity in Vitro and in Vivo — in vitro / mouse in vivoView study →}.

In rats, sterubin (10 mg/kg) improved behaviour and reversed oxidative and inflammatory markers in scopolamine-induced memory impairment ^{7Reference 7Kazmi I et al. · 2023AnimalSterubin protects against chemically-induced Alzheimer’s disease by reducing biomarkers of inflammation and oxidative stress in rats — animal model (rat)View study →} and in rotenone-induced Parkinson’s disease ^{8Reference 8Alqurashi MM et al. · 2024AnimalProtective effect of sterubin against neurochemical and behavioral impairments in rotenone-induced Parkinson’s disease — animal model (rat)View study →}.

Across leaf extracts of 14 Eriodictyon taxa from herbarium specimens, neuroprotective potency tracked sterubin content but not eriodictyol or homoeriodictyol ^{5Reference 5Maher P et al. · 2020In vitroThe Value of Herbarium Collections to the Discovery of Novel Treatments for Alzheimer’s Disease, a Case Made With the Genus Eriodictyon — in vitroView study →}. Sterubin also restores mitochondrial function in nerve cells under oxidative stress ^{4Reference 4Goujon M et al. · 2024In vitroThe Neuroprotective Flavonoids Sterubin and Fisetin Maintain Mitochondrial Health under Oxytotic/Ferroptotic Stress in HT22 Neuronal Cells — in vitroView study →}.

Gap: every finding is cell-based or rodent — there is no human neuroprotection or cognition trial, and because sterubin content is chemotype-dependent, a given batch of leaf may contain almost none of the active compound.

Sterubin strongly suppresses inflammatory activation in brain microglia, in step with Nrf2 induction ^{3,5Reference 3Liang Z et al. · 2022In vitroStructural Requirements for the Neuroprotective and Anti-Inflammatory Activities of the Flavanone Sterubin — in vitroView study →Reference 5Maher P et al. · 2020In vitroThe Value of Herbarium Collections to the Discovery of Novel Treatments for Alzheimer’s Disease, a Case Made With the Genus Eriodictyon — in vitroView study →}.

A high-throughput screen of more than 1,400 natural products in activated macrophages and microglia found E. californicum among the few valid anti-inflammatory hits ^{9Reference 9Mazzio EA et al. · 2016In vitroNatural product HTP screening for antibacterial (E. coli O157:H7) and anti-inflammatory agents in activated macrophages and microglial cells — in vitroView study →}. A flavanone-rich extract of the related E. angustifolium lowered IL-6 release by up to 52% in stimulated human gum fibroblasts ^{10Reference 10Walker J et al. · 2016In vitroIdentification of an anti-inflammatory potential of Eriodictyon angustifolium compounds in human gingival fibroblasts — in vitroView study →}.

In the rat Alzheimer’s and Parkinson’s models, sterubin lowered TNF-α, IL-6, IL-1β and NF-κB ^{7,8Reference 7Kazmi I et al. · 2023AnimalSterubin protects against chemically-induced Alzheimer’s disease by reducing biomarkers of inflammation and oxidative stress in rats — animal model (rat)View study →Reference 8Alqurashi MM et al. · 2024AnimalProtective effect of sterubin against neurochemical and behavioral impairments in rotenone-induced Parkinson’s disease — animal model (rat)View study →}.

The fibroblast work used E. angustifolium, and no anti-inflammatory endpoint has been tested in people.

The leaf is rich in phenolics; rosmarinic acid alone runs 22–53 mg/g ^{1Reference 1Satyal P et al. · 2026Chemical Composition of Eriodictyon californicum (California Yerba Santa) Cultivated in Ontario, Oregon, USA — analytical/phytochemistryView study →}. A proprietary “Santa herba” extract had an ORAC value of 819 Trolox equivalents ^{11Reference 11Mödinger Y et al. · 2021RCTA Food Supplement with Antioxidative Santa Herba Extract Modulates Energy Metabolism and Contributes to Weight Management — randomised placebo-controlled clinical trialView study →}.

Sterubin strongly activates Nrf2, the regulator of the cell’s own antioxidant defences, in nerve and microglial cells ^{2,3Reference 2Fischer W et al. · 2019In vitroOld age-associated phenotypic screening for Alzheimer’s disease drug candidates identifies sterubin as a potent neuroprotective compound from Yerba santa — in vitro screeningView study →Reference 3Liang Z et al. · 2022In vitroStructural Requirements for the Neuroprotective and Anti-Inflammatory Activities of the Flavanone Sterubin — in vitroView study →}. It protects nerve cells against oxytosis and ferroptosis, an iron-dependent form of oxidative cell death, and preserves mitochondrial redox balance under that stress ^{4,5Reference 4Goujon M et al. · 2024In vitroThe Neuroprotective Flavonoids Sterubin and Fisetin Maintain Mitochondrial Health under Oxytotic/Ferroptotic Stress in HT22 Neuronal Cells — in vitroView study →Reference 5Maher P et al. · 2020In vitroThe Value of Herbarium Collections to the Discovery of Novel Treatments for Alzheimer’s Disease, a Case Made With the Genus Eriodictyon — in vitroView study →}.

In the rat neurodegeneration models, sterubin raised SOD, glutathione and catalase and lowered malondialdehyde ^{7,8Reference 7Kazmi I et al. · 2023AnimalSterubin protects against chemically-induced Alzheimer’s disease by reducing biomarkers of inflammation and oxidative stress in rats — animal model (rat)View study →Reference 8Alqurashi MM et al. · 2024AnimalProtective effect of sterubin against neurochemical and behavioral impairments in rotenone-induced Parkinson’s disease — animal model (rat)View study →}.

The one human study measured weight, not oxidative-stress markers.

A 12-week randomised, placebo-controlled trial gave a food supplement containing a “Santa herba” (E. californicum) extract to 49 women, 24 overweight and 25 with obesity (mean age 47.5). In the women with obesity, body weight (P = 0.042) and body fat (P = 0.044) fell compared with placebo, and leptin showed a downward trend (P = 0.065) ^{11Reference 11Mödinger Y et al. · 2021RCTA Food Supplement with Antioxidative Santa Herba Extract Modulates Energy Metabolism and Contributes to Weight Management — randomised placebo-controlled clinical trialView study →}.

In laboratory work in the same paper, the extract bound the adenosine A2A receptor and increased the movement of C. elegans worms by 7.5% ^{11Reference 11Mödinger Y et al. · 2021RCTA Food Supplement with Antioxidative Santa Herba Extract Modulates Energy Metabolism and Contributes to Weight Management — randomised placebo-controlled clinical trialView study →}. The trial is registered as NCT03853603.

Gap: a single small trial, in one sex, of a specific proprietary extract, with the effect confined to a subgroup and some endpoints only at trend level. It does not transfer to leaf tea.

Eriodictyol, a flavanone found in yerba santa and other plants, inhibited mast-cell degranulation in vitro. It suppressed β-hexosaminidase release and IL-4 expression by reducing ceramide kinase, and it dampened a passive cutaneous anaphylaxis reaction in mice ^{12Reference 12Yoo JM et al. · 2012In vitroInhibitory effect of eriodictyol on IgE/Ag-induced type I hypersensitivity — in vitro / animal modelView study →}.

Gap: the work is on isolated eriodictyol, not yerba santa extract, and eriodictyol is widespread across the plant kingdom — the finding says little specific about the herb, and there is no human allergy data.

Activity-guided fractionation of E. californicum isolated twelve flavonoids, including eriodictyol, homoeriodictyol, sakuranetin and chrysin, that inhibited the metabolism of the carcinogen benzo[a]pyrene by hamster embryo cells ^{13Reference 13Liu YL et al. · 1992In vitroIsolation of potential cancer chemopreventive agents from Eriodictyon californicum — in vitroView study →}.

In rats given a chemical colon carcinogen, eriodictyol (200 µg/kg) reduced aberrant crypt foci, polyp incidence and oxidative stress ^{14Reference 14Mariyappan P et al. · 2017AnimalEffect of eriodictyol on preneoplastic lesions, oxidative stress and bacterial enzymes in 1,2-dimethylhydrazine-induced colon carcinogenesis — animal model (rat)View study →}.

All of this is in vitro or single-animal-model work on individual constituents, some of which, like eriodictyol, are not unique to the herb. No whole-herb or human evidence exists.

Antibacterial activity was reported in a 1951 study of E. californicum ^{15Reference 15Salle AJ et al. · 1951In vitroStudies on the antibacterial properties of Eriodictyon californicum — in vitroView study →}.

A modern screen of more than 1,400 natural products against enterohemorrhagic E. coli O157:H7 did not list yerba santa among the products that killed the bacterium at under 100 µg/mL ^{9Reference 9Mazzio EA et al. · 2016In vitroNatural product HTP screening for antibacterial (E. coli O157:H7) and anti-inflammatory agents in activated macrophages and microglial cells — in vitroView study →}.

There is no comparison against reference antibiotics and no in vivo follow-up.

Coughs, colds, chest infections and asthma are the plant’s main traditional uses ^{1,21Reference 1Satyal P et al. · 2026Chemical Composition of Eriodictyon californicum (California Yerba Santa) Cultivated in Ontario, Oregon, USA — analytical/phytochemistryView study →Reference 21Howard · 1992Eriodictyon californicum, California yerba santaView study →}. The leaf’s essential oil is often rich in 1,8-cineole, whose mucolytic and expectorant activity has been studied mainly in other plants, such as eucalyptus. Both the oil yield and its cineole content vary widely between plants ^{1Reference 1Satyal P et al. · 2026Chemical Composition of Eriodictyon californicum (California Yerba Santa) Cultivated in Ontario, Oregon, USA — analytical/phytochemistryView study →}.

Gap: there is no clinical or even animal study of yerba santa itself as an expectorant; the case is ethnobotanical plus a plausible marker compound, which is why the score is low despite this being the popular headline use.

Skin reactions. Allergic contact dermatitis is well documented for the related Eriodictyon parryi (poodle-dog bush), especially after it blooms following wildfire ^{18Reference 18Czaplicki CD · 2013Case reportContact dermatitis from Eriodictyon parryi: a novel cause of contact dermatitis in California — case reportView study →}. The resinous leaves of yerba santa may cause similar reactions in sensitive people.

Interactions. No human toxicity, drug-interaction or organ-toxicity studies of E. californicum have been published. The leaf flavonoids affected carcinogen-metabolising enzymes in cells ^{13Reference 13Liu YL et al. · 1992In vitroIsolation of potential cancer chemopreventive agents from Eriodictyon californicum — in vitroView study →}, but no clinical interaction has been shown.

Variable content. Sterubin ranges from none to about 7% of the dry leaf between plants, so no particular active-compound content can be assumed ^{1Reference 1Satyal P et al. · 2026Chemical Composition of Eriodictyon californicum (California Yerba Santa) Cultivated in Ontario, Oregon, USA — analytical/phytochemistryView study →}.