# Ouabain (Strophanthus gratus)

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/ouabain-strophanthus-gratus
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-04-02
**Evidence Score:** 1 / 10
**Category:** Compound
**Also Known As:** Strophanthus gratus glycoside, g-strophanthin, ouabaine, acocantherin, Strodival (historical pharmaceutical)

## Overview

Ouabain (C₂₉H₄₄O₁₂) is a rhamnose-ouabagenin glycoside that exerts its primary pharmacological effects by binding and inhibiting the Na⁺/K⁺-ATPase pump, elevating intracellular Na⁺ and Ca²⁺ to enhance cardiac contractility. Clinically, plasma ouabain inversely correlated with cardiac index (r = -0.62, p < 0.005) in 51 heart failure patients, identifying endogenous ouabain as a potential biomarker of [cardiovascular](/ingredients/condition/heart-health) dysfunction rather than an established therapeutic agent.

## Health Benefits

- **Positive Inotropic Effect**: Ouabain inhibits cardiac Na⁺/K⁺-ATPase, raising intracellular Ca²⁺ via the Na⁺/Ca²⁺ exchanger, augmenting actin-myosin cross-bridge cycling and myocardial contractile force at controlled doses.
- **[Anti-Inflammatory](/ingredients/condition/inflammation) Activity**: In preclinical models, nanomolar ouabain reduced TNF-α by 57% and IL-1β by 58%, and decreased inflammatory cell infiltration by 46% with 33% less exudation, suggesting modulation of NF-κB-dependent pathways.
- **Anti-Cancer Cell Migration**: Picomolar concentrations (10–30 pM) inhibited lung cancer H292 cell migration in vitro by suppressing integrin subunits α4, α5, αv, β3, and β4, disrupting extracellular matrix adhesion and cytoskeletal signaling.
- **Endogenous Hormonal Signaling**: As an endogenous hormone produced in adrenal glands, circulating ouabain at physiological picomolar-to-low-nanomolar concentrations (30–380 pM in healthy adults) participates in [blood pressure regulation](/ingredients/condition/heart-health) and sodium homeostasis via renal Na⁺/K⁺-ATPase modulation.
- **Reproductive Biology Modulation**: Nanomolar ouabain inhibits sperm motility by disrupting ionic gradients essential for flagellar movement, and at 10⁻⁸ M reduces placental sFlt1 production dose-dependently, implicating it in placental vascular regulation.
- **Biphasic Cell Proliferation Regulation**: At low subnanomolar concentrations, ouabain paradoxically stimulates cell growth via Na⁺/K⁺-ATPase-coupled receptor signaling (including Src kinase and EGFR transactivation), while high doses inhibit proliferation or induce apoptosis through sustained pump inhibition.
- **Cardiovascular Biomarker Potential**: Elevated endogenous plasma ouabain (mean 1.59 nM vs. 0.44 nM in controls) in heart failure patients provides a measurable correlate of hemodynamic compromise, with potential diagnostic utility pending prospective validation.

## Mechanism of Action

Ouabain binds with high affinity to the extracellular face of the α-subunit of Na⁺/K⁺-ATPase, stabilizing the E2-P conformation and preventing dephosphorylation, thereby blocking the enzyme cycle and reducing Na⁺ efflux and K⁺ influx across the plasma membrane. The resulting rise in intracellular Na⁺ diminishes the Na⁺ gradient driving the Na⁺/Ca²⁺ exchanger (NCX), causing intracellular Ca²⁺ accumulation that activates troponin C and enhances myofilament force generation in cardiomyocytes. Beyond direct pump inhibition, ouabain initiates Na⁺/K⁺-ATPase-dependent signal transduction cascades: the α1 isoform scaffolds with Src kinase, caveolin-1, and EGFR, activating Ras/ERK and PI3K/Akt pathways that regulate gene expression for cell growth, survival, and [inflammation](/ingredients/condition/inflammation). At nanomolar concentrations relevant to endogenous physiology, these non-canonical signaling functions may predominate, explaining the biphasic dose-response and the compound's roles in [blood pressure regulation](/ingredients/condition/heart-health), natriuresis, and possibly tumor cell behavior.

## Clinical Summary

No prospective interventional clinical trials have established a therapeutic dose or confirmed efficacy of exogenous ouabain in human [cardiovascular](/ingredients/condition/heart-health) disease, oncology, or [inflammation](/ingredients/condition/inflammation) management. The primary human data consist of the observational correlation study (n=70 total) linking elevated endogenous plasma ouabain to reduced cardiac index and arterial pressure in heart failure, which identifies an association rather than a causal therapeutic relationship. Historically, ouabain was administered intravenously as a rapid-acting cardiac glycoside for acute heart failure in the 20th century, but it was superseded by digoxin due to its extremely narrow therapeutic index and unpredictable toxicity. Confidence in any clinical benefit from exogenous ouabain administration remains very low given the absence of modern RCTs, the toxicity risks at doses approaching efficacy thresholds, and the preclinical nature of most mechanistic findings.

## Nutritional Profile

Ouabain is a pure pharmacological compound (C₂₉H₄₄O₁₂, MW 584.7 g/mol) and not a nutritional ingredient; it contributes no macronutrients, vitamins, or dietary minerals. Its structure consists of a steroidal aglycone (ouabagenin) linked to L-rhamnose, a 6-deoxy sugar, conferring its glycoside pharmacokinetics including moderate water solubility (~10 mg/mL) and resistance to hepatic first-pass [metabolism](/ingredients/condition/weight-management) relative to some other glycosides. Plasma recovery in analytical extraction protocols reaches approximately 90% by HPLC with fluorescence or mass spectrometric detection, indicating reasonable but not complete systemic stability. No dietary sources contribute meaningful ouabain intake; endogenous biosynthesis from cholesterol precursors in the adrenal gland represents the primary physiological source in humans.

## Dosage & Preparation

- **Historical Intravenous Injection**: Pharmaceutical-grade ouabain was administered IV at doses of 0.25–0.5 mg for acute cardiac decompensation; this route is now largely obsolete in Western medicine.
- **Endogenous Physiological Range**: In healthy humans, circulating endogenous ouabain measures 30–380 pM (mean ~0.44 nM); no exogenous dosing strategy reliably reproduces these concentrations without toxicity risk.
- **Oral Bioavailability**: Oral absorption is poor and erratic due to limited gastrointestinal uptake; no standardized oral supplement form or dose has been validated in human clinical trials.
- **In Vitro Effective Concentrations**: Preclinical studies demonstrate activity at 10–30 pM (anti-migration), 10⁻⁸ M (sperm motility inhibition, sFlt1 suppression), and nanomolar ranges for [anti-inflammatory](/ingredients/condition/inflammation) effects — none directly translatable to human supplementation doses.
- **Standardization**: No commercial supplement standardization exists; pharmaceutical preparations are expressed as pure compound mass (mg); plant-extracted forms from Strophanthus gratus seeds are not standardized for over-the-counter use.
- **No Recommended Supplemental Dose**: Regulatory agencies (FDA, EMA) have not approved ouabain as a dietary supplement or nutraceutical; no safe supplemental dose range has been established for human self-administration.

## Safety & Drug Interactions

Ouabain carries a high and well-documented toxicity risk due to its narrow therapeutic index: doses approaching efficacy thresholds inhibit Na⁺/K⁺-ATPase sufficiently to cause life-threatening ventricular arrhythmias, hyperkalemia, heart block, nausea, vomiting, and visual disturbances, mirroring digitalis glycoside toxicity. Significant drug interactions arise through shared organic anion transport proteins (SLC22A8, SLCO4C1, SLCO1B3), which govern renal and hepatic elimination; concurrent use of other cardiac glycosides (digoxin), diuretics causing electrolyte imbalances, and drugs that inhibit these transporters can precipitate toxicity at otherwise subtherapeutic doses. Ouabain is contraindicated in patients with ventricular arrhythmias, hypertrophic obstructive cardiomyopathy, hypokalemia, hypercalcemia, and renal failure, and its paradoxical elevation in heart failure patients (mean 1.59 nM) suggests caution in any [cardiovascular](/ingredients/condition/heart-health) disease context. No safety data exist for use during pregnancy or lactation; ouabain's inhibitory effects on placental sFlt1 production and sperm motility at nanomolar concentrations indicate potential reproductive toxicity, and it should be considered contraindicated in these populations absent controlled clinical evidence.

## Scientific Research

The clinical evidence base for ouabain as a therapeutic or nutritional agent is extremely limited; no completed randomized controlled trials have evaluated exogenous ouabain supplementation in humans, and ClinicalTrials.gov listings lack published results with defined sample sizes or effect sizes. The most substantive human observational data derive from a small cohort study of 51 heart failure patients versus 19 healthy controls, which documented significant inverse correlations between plasma ouabain and cardiac index (r = -0.62, p < 0.005) and mean arterial pressure (r = -0.51, p < 0.05), suggesting endogenous ouabain rises as a compensatory or pathological response to hemodynamic stress. Preclinical in vitro evidence is more extensive, demonstrating anti-migratory effects at 10–30 pM in H292 lung cancer cells, [anti-inflammatory](/ingredients/condition/inflammation) cytokine reduction (TNF-α −57%, IL-1β −58%) in cell culture models, and dose-dependent suppression of placental sFlt1, but these findings have not been translated to human trials. Overall, the evidence is preclinical and observational in nature, with mechanistic plausibility but no human efficacy or safety data sufficient to support therapeutic use outside historical intravenous [cardiovascular](/ingredients/condition/heart-health) contexts.

## Historical & Cultural Context

In East and Central Africa, indigenous hunters prepared ouabain-rich extracts from Strophanthus gratus seeds and Acokanthera schimperi bark by boiling or cold aqueous extraction, applying the concentrated paste to arrow tips for hunting large game and, in some traditions, as a purported antidote for snakebites. The compound was introduced to European pharmacopoeia around 1882 by Thomas Fraser, who systematically studied Strophanthus and proposed it as an alternative to digitalis for cardiac conditions, leading to its adoption as a rapid-acting intravenous cardiostimulant in European hospitals through much of the early-to-mid 20th century. Soviet and East German physicians reportedly continued using oral ouabain preparations (marketed as 'Strodival' or g-strophanthin) into the late 20th century for angina and heart failure, a practice largely unrecognized in Anglophone clinical literature. The discovery in the 1990s that mammals, including humans, endogenously synthesize and secrete ouabain-like substances from the adrenal cortex and hypothalamus fundamentally reframed it from purely exogenous poison to endogenous steroid hormone, opening a new chapter of physiological research.

## Synergistic Combinations

No evidence-based synergistic supplement combinations have been established for ouabain due to the absence of human clinical trials; combining ouabain with other cardiac glycosides such as digoxin or digitoxin would be expected to produce additive Na⁺/K⁺-ATPase inhibition and compounded toxicity risk rather than therapeutic benefit. In preclinical oncology contexts, ouabain's integrin-suppressing and anti-migratory actions have been hypothesized to complement conventional cytotoxic agents by targeting adhesion-dependent survival pathways, but no co-administration data in humans exist. Potassium supplementation is mechanistically relevant as a competitive antagonist at the K⁺-binding site of Na⁺/K⁺-ATPase, theoretically mitigating toxicity at borderline inhibitory ouabain concentrations, a principle well-established in cardiac glycoside toxicity management.

## Frequently Asked Questions

### What is ouabain and how does it work in the body?

Ouabain is a cardiac glycoside (C₂₉H₄₄O₁₂) derived from Strophanthus gratus seeds and also produced endogenously in human adrenal glands at physiological plasma levels of 30–380 pM. It works primarily by binding the α-subunit of Na⁺/K⁺-ATPase, blocking the ion pump and raising intracellular Na⁺ and Ca²⁺, which increases cardiac muscle contractility. At low nanomolar concentrations, it also activates secondary signaling cascades including Src kinase, ERK, and PI3K/Akt pathways that influence cell growth and inflammation.

### Is ouabain safe to take as a supplement?

Ouabain is not approved as a dietary supplement by the FDA or EMA, and it carries significant toxicity risks due to its extremely narrow therapeutic index. Doses approaching pharmacological effect can cause life-threatening ventricular arrhythmias, hyperkalemia, and heart block, identical in profile to digitalis toxicity. No safe supplemental dose has been established in human clinical trials, and self-administration is strongly inadvisable without medical supervision.

### What is endogenous ouabain and is it different from the plant compound?

Endogenous ouabain is a hormone-like substance biosynthesized from cholesterol precursors in the adrenal cortex and hypothalamus of humans and other mammals, circulating at 30–380 pM in healthy individuals. Research in the 1990s confirmed its structural identity to plant-derived ouabain from Strophanthus gratus, though biosynthetic pathway details remain incompletely characterized. Elevated endogenous ouabain (mean 1.59 nM) in heart failure patients suggests a pathophysiological role in sodium retention and hemodynamic compensation rather than a beneficial adaptive response.

### Has ouabain been tested in clinical trials for cancer or heart disease?

Ouabain appears in clinical trial registries but no completed trials have published results with defined sample sizes and effect sizes for therapeutic use. The strongest human evidence is an observational study of 51 heart failure patients showing plasma ouabain inversely correlated with cardiac index (r = -0.62, p < 0.005), establishing it as a biomarker rather than a validated treatment. Preclinical data show anti-migratory effects on lung cancer cells at 10–30 pM and anti-inflammatory cytokine reductions of 57–58%, but human translation remains undemonstrated.

### What plant does ouabain come from and how was it traditionally used?

Ouabain is sourced primarily from the seeds of Strophanthus gratus and the bark of Acokanthera schimperi, both native to East and Central Africa. Indigenous communities prepared concentrated aqueous or boiled extracts applied to arrow tips for hunting and warfare, and the compound was reputed as an antidote for snakebites in some traditions. European physicians adopted it as an intravenous cardiac stimulant in the late 19th and early 20th centuries, and Soviet-era medicine used oral ouabain preparations (g-strophanthin) for angina through the 1990s.

### Does ouabain have drug interactions with heart medications like digoxin or ACE inhibitors?

Ouabain shares the same Na⁺/K⁺-ATPase mechanism as cardiac glycosides like digoxin, creating significant interaction potential and risk of additive toxicity when combined. Concurrent use with ACE inhibitors, beta-blockers, or diuretics may alter potassium balance and ouabain efficacy, requiring careful medical monitoring. Due to these serious interaction risks, ouabain should only be used under direct medical supervision if prescribed alongside any cardiovascular medications.

### What is the difference between ouabain from Strophanthus gratus and synthetic ouabain?

Both plant-derived and synthetic ouabain contain the identical active C29H44O12 compound with equivalent pharmacological effects on cardiac contractility and Na⁺/K⁺-ATPase inhibition. The distinction lies in extraction method and purity rather than biological activity—synthetic forms may offer standardized dosing while plant extracts contain additional co-compounds. Both forms carry the same safety concerns and contraindications, making the choice primarily a matter of manufacturing consistency.

### Who should avoid ouabain supplementation and what are the contraindications?

Ouabain is contraindicated in individuals with hypokalemia (low potassium), hyperkalemia, heart rhythm disorders, acute myocardial infarction, or renal impairment, as these conditions elevate toxicity risk. Pregnant and nursing women should avoid ouabain due to lack of safety data and potential cardiac effects on fetal development. Patients taking digoxin, other cardiac glycosides, or medications affecting potassium levels must not use ouabain without explicit medical guidance.

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