Andrographis, andrographolide, NF-κB p50, and acute respiratory infection evidence

Andrographis paniculata is a medicinal plant, while andrographolide is one of its diterpenoids. They are not interchangeable: a leaf extract is a mixture, a standardized product has its own composition, and purified andrographolide used in an experiment is a distinct molecule. This distinction matters when assessing claims about NF-κB inhibition. A cellular mechanism for a pure compound does not show that taking a particular extract produces that concentration in the airways or prevents viral infection.

This article reviews the chemistry of the plant and its extracts, a proposed covalent interaction with NF-κB p50, other preclinical targets, limited pharmacokinetic evidence, trials of acute respiratory infection (ARI) symptoms, and a serious allergy-safety signal. The clinical conclusion depends on the specific product: trials tested particular extracts, fixed combinations, or plant powder, not “andrographis” as a uniform class.

1. Plant, extract, and molecule are three different things

King of bitters (Andrographis paniculata, family Acanthaceae) is an herb used in South and Southeast Asian traditions. The English trade name “king of bitters” describes its pronounced bitterness, not its pharmacological strength. For a supplement, the plant part, source and harvest of the raw material, extraction solvent, dry-extract yield, marker profile, and batch stability matter. The label “andrographis extract” without these details does not specify a chemical dose.

The main studied constituents are labdane diterpenoid lactones. They include andrographolide, 14-deoxy-11,12-didehydroandrographolide, 14-deoxyandrographolide, neoandrographolide, and related compounds; the plant also contains diterpenoid glycosides and flavonoids. Their proportions vary with cultivar or chemotype, plant organ, growing conditions, harvest time, and extraction method. “Total andrographolides” and the amount of andrographolide itself are therefore different measurements.

Andrographolide is a labdane diterpenoid with molecular formula C₂₀H₃₀O₅ and molar mass of about 350.45 g/mol. Its scaffold has several hydroxyl groups and an unsaturated γ-lactone. The electrophilic lactone helps explain reactivity with thiols in model systems, but it does not mean that the compound selectively alkylates the same protein target in every tissue. At high concentrations, reactive natural molecules may also interact with other accessible nucleophilic groups.

Quality control requires confirmation of botanical identity and a suitable analytical method, such as HPLC with appropriate standards or LC–MS. One must check what is included in the marker total and whether the percentage is calculated on a dry-weight basis; testing one marker does not guarantee the absence of adulterants, contaminants, or mislabelling. Manufacturer standardization is a property of the product and its quality-control method, not proof of clinical efficacy.

2. NF-κB: where andrographolide’s proposed effect sits

NF-κB is a family of transcription factors that regulate inflammatory, immune, and stress responses. A common dimer in the canonical pathway is p50/RelA (p65). Signals from TNF and IL-1 receptors, Toll-like receptors, and some other receptors can activate the IKK complex. IKKβ, together with IKKα and NEMO, phosphorylates the inhibitor IκBα; after ubiquitination, IκBα is degraded by the proteasome. The freed NF-κB dimer enters the nucleus and binds κB DNA sequences. Viral sensing through TLR3/TLR7 and RIG-I/MDA5 uses several overlapping cascades; it is not one linear route for every virus and cell.

The p50 subunit is produced by processing its p105 precursor and contains a Rel-homology region involved in dimerization and DNA binding. p50 lacks RelA’s classical transactivation domain, so the outcome depends on its dimer partner and cofactors. Thus, “NF-κB activation” does not always mean one gene set or only increased inflammation.

In the primary study by Xia and colleagues, purified andrographolide formed a covalent adduct with reduced p50 Cys62; in the cell systems studied, this interfered with NF-κB binding to a DNA oligonucleotide. The authors observed suppression of selected induced responses, including E-selectin expression in endothelial cells, while IκBα degradation, nuclear translocation of p50/p65, and cell growth were preserved under the conditions used. This is an important molecular finding, but its scope is limited to a particular compound, experimental concentration, cell type, and measured genes.

Chemically, andrographolide’s reactive unsaturated lactone is compatible with bond formation with a cysteine thiol. The study established a covalent adduct and a role for Cys62 in the described mechanism; it does not show that an oral extract dose reaches the necessary concentration in human airway mucosa. Structural crystals of DNA-bound p50 or p50/p65 describe protein architecture and DNA contacts; by themselves they are not a crystal structure of an “andrographolide–p50” complex. The precise geometry of DNA displacement, stereoselectivity, a universal kinetic constant, and selectivity across the proteome should therefore not be inferred from one reaction diagram.

The illustrated mechanism is downstream of nuclear translocation, at the DNA-binding protein’s contact with a promoter. It differs from blocking IKK, stabilizing IκBα, or broadly inhibiting the proteasome. This distinction helps separate mechanisms in an experiment, but it does not prove the absence of systemic immunosuppression or safety in people. NF-κB regulates cell survival, barrier function, and antimicrobial defense as well as pro-inflammatory cytokines; clinical significance requires outcome and safety measurements.

Cys62 and the biological reaction: what is known and what remains a model

The cysteine in p50’s active site matters for protein–DNA interaction and sensitivity to redox state. The mechanism can be represented schematically as covalent interaction of a reduced thiol with an electrophilic part of the molecule:

p50–Cys62–SH + andrographolide ⇌ modified p50 + environmental products

The arrow does not specify an in vivo equilibrium or imply that the reaction is necessarily reversible; it denotes only the thiol chemistry studied experimentally. Covalent binding should not be confused with competitive ligand binding in a receptor pocket or a decrease in p50 concentration. Genetic substitution of Cys62, biochemical detection of modification, and functional binding assays support a role for this residue in the studied model. They do not establish selectivity in every cell type or a therapeutic window for an oral botanical product.

In the body, cytosolic and nuclear compound concentrations depend on dissolution, intestinal absorption, metabolism, distribution, protein binding, and excretion. A reactive lactone may also be consumed by other thiols or metabolized before reaching the nucleus. Molecular plausibility and clinically achievable exposure are separate questions.

3. Other targets: preclinical branches, not one “immune effect”

Changes in Nrf2/ARE, NLRP3, STAT3, MAPK, AP-1, iNOS, and leukocyte responses have been reported for andrographolide and other diterpenoids. Most observations come from cell cultures or animal models of inflammation, lung injury, asthma, colitis, and infection. The free-compound concentration in a model often differs from exposure after a food or supplement product; several processes may change at once, and one marker does not identify a single causal target.

In some models, andrographolide has been associated with Nrf2-dependent antioxidant responses and altered Nrf2–Keap1 interaction. Findings about particular Keap1 cysteines cannot be transferred to all tissues and products without direct testing of the adduct and exposure. A change in nuclear Nrf2, HO-1, or antioxidant activity in a mouse does not prove that lung injury is prevented or recovery from an ARI is faster in a patient.

Inhibition of NLRP3 assembly or activation has also been described in cell and animal models, along with changes in JAK/STAT3, T-cell differentiation, and mediator production. Findings in colitis or experimental asthma do not establish treatment of a respiratory viral infection. Signalling is especially model-dependent: dose, stimulation regimen, animal species, cell type, and route determine which part of a cascade changes.

Antiviral findings are also heterogeneous. Replication of influenza virus has been studied in cells and animals using the pure compound or selected derivatives; SARS-CoV-2 work includes enzyme and cell models, including interaction with Mpro. Virtual docking is a hypothesis, and a lower viral signal in culture is not equivalent to preventing infection, eradicating a virus, or reducing hospitalizations in people. Unless a specific botanical form is confirmed in a clinical trial with laboratory-confirmed virus and a relevant outcome, it should not be described as having proven clinical antiviral action.

Why evidence for a pure compound does not describe an extract

A dry extract may contain several diterpenoids with different solubility, reactivity, and pharmacokinetics, as well as other phytochemicals. A standardized product is characterized only by the measure used to test it; total lactones do not equal pure andrographolide content. A combination adds another layer: without comparisons against its ingredients separately, an effect of a fixed product cannot be attributed to one component.

To connect a molecular mechanism to a clinical outcome, studies need actual exposure measurements, a validated target marker in relevant tissue, an appropriate control, and a prespecified patient outcome. A reduction in a cytokine, iNOS expression, or laboratory marker does not replace symptom duration, complications, functional recovery, or safety. Until such evidence chains are complete, the accurate statement is that a mechanism was shown in a particular system, not that it explains supplement benefit.

4. Pharmacokinetics and why doses cannot be converted between products

Oral bioavailability of andrographolide is limited by several steps: dissolution from a solid form, passage across intestinal epithelium, presystemic metabolism, and efflux. Rat and cell-model experiments have noted rapid conversion to conjugated metabolites and P-glycoprotein-mediated transport back into the intestinal lumen. These findings may explain low levels of parent compound in plasma, but they cannot be directly converted into a numerical human bioavailability. A pharmacokinetic study of the fixed Kan Jang combination likewise does not make its profile equivalent to purified andrographolide.

Conjugation, including glucuronidation and sulfation, has been described in the body, and andrographolide metabolites have been detected in human urine. Enzyme studies with human microsomes suggest that UGT and some CYP isoforms may be involved. This does not establish a clinical interaction with every medicine that is a substrate of the same enzyme; that requires human data on concentrations, in vivo inhibition or induction, and changes in drug exposure.

Formulations using liposomes, nanoemulsions, phospholipid complexes, cyclic sugars, and other carriers are being studied to change dissolution and absorption. Greater systemic exposure may also change the risk profile. Evidence for a bioenhancer in a cell or animal model does not justify routinely combining andrographis with piperine, quercetin, or grapefruit: such combinations may alter the metabolism of other medicines, and no clinical dose or benefit of such a combination for ARI has been established.

Milligrams of different products are therefore not interchangeable. Powder cannot be converted to extract by total mass alone, and a percentage of total diterpenes cannot be converted to a dose of pure andrographolide without batch analysis. Doses below describe research regimens, not a self-treatment plan.

5. Clinical evidence in ARI: specific products and outcomes

Andrographis trials have usually measured symptom severity in uncomplicated upper respiratory infection or pharyngotonsillitis. These outcomes differ from laboratory confirmation of a specific virus, infection prevention, pneumonia prevention, reduced antibiotic use, or fewer hospitalizations. Results from a product containing eleuthero especially cannot be attributed to andrographis alone.

Reviews and meta-analyses have described possible symptom reduction in uncomplicated ARI, but pooled estimates combine different products, doses, age groups, scales, control interventions, and assessment times. Older studies are small and do not always describe product standardization or outcome registration in detail. Even a statistically significant symptom effect does not by itself show how noticeable it is to patients, whether it prevents complications, or whether another manufacturer’s product reproduces it.

None of the studies listed establishes a universal dose of “pure andrographolide” for all forms and indications. Fixed-combination trials included eleuthero; the plant-powder study measured grams of raw material; AP-Bio/KalmCold studies tested the mass of a particular extract; and Bio-Immune tested a separate standardized formula. These interventions should not be collapsed into one dose scale.

A clinical signal does not establish NF-κB as the mediator

The clinical trials above assessed symptoms and, in part, general inflammatory markers. They did not show that participants reached tissue andrographolide concentrations sufficient to modify p50 Cys62, and they did not measure target engagement in airway mucosa. A molecular diagram may explain a laboratory effect, but a particular extract’s clinical result may involve many components or mechanisms—or may not reproduce in other populations.

Evidence for pharyngitis, colds, and seasonal prevention should be considered separately. A short symptom trial does not establish infection prevention. A school pilot with a fixed mixture does not define a long preventive course for adults. Viral replication in vitro does not show treatment of COVID-19, influenza, or RSV in a patient. Conclusions about a specific virus require appropriate laboratory confirmation, clinical controls, and prespecified outcomes.

6. Safety: anaphylaxis and taste disturbance are not minor issues

Short trials often reported good tolerability and mild gastrointestinal symptoms, but a few hundred participants cannot rule out rare severe allergy. Urticaria, swelling, bronchospasm, and anaphylaxis have been described after medicines containing Andrographis. A reaction may occur after earlier courses were tolerated; some reports involved several plants, so an individual case may not identify the causal ingredient. Nevertheless, the regulator treats the risk as significant.

According to Australia’s TGA, 287 reports of anaphylaxis associated with andrographis-containing medicines had been received by the end of 2025; the reports included one fatal case in 2024. These are pharmacovigilance reports without a denominator of exposed users: they cannot establish incidence, prove causation in each case, or be generalized to all countries and formulations. In September 2026, however, the TGA excluded andrographis from ingredients permitted for new low-risk listed medicines in Australia because it considered the risk of severe allergy insufficiently manageable in that regulatory category. This is a jurisdiction-specific decision; it does not mean all existing products have simultaneously been withdrawn worldwide.

The TGA separately warns about taste disturbance or loss with medicines containing andrographis. Infection itself can affect taste, but the regulator considered the reports and clinical data sufficient to warrant a warning. Stop taking a product if an allergic reaction occurs; breathing difficulty, tongue or throat swelling, severe dizziness, or collapse requires emergency care. Tolerating an initial dose does not guarantee that a later dose will be tolerated.

Interaction claims need careful wording. Extracts and individual diterpenoids have affected CYP or platelet responses in laboratory and animal models; the clinical magnitude for a particular medicine in people is generally unknown. Do not declare every CYP3A4- or CYP2C9-metabolized medicine incompatible with andrographis on the basis of an in vitro IC₅₀, and do not promise that interactions are absent. People regularly using anticoagulants, antiplatelet drugs, glucose-lowering medicines, immunosuppressants, or medicines with a narrow therapeutic range should show the supplement’s composition to a clinician or pharmacist before use.

Evidence is insufficient to independently transfer adult doses of specific standardized extracts to pregnancy, breastfeeding, or children. This establishes neither universal toxicity nor safety. Product choice should account for local registration, composition, allergy history, and alternatives; a botanical extract should not replace prescribed treatment for an infection.

7. How to read the evidence and what can be concluded

For clinical interpretation, first identify the material: plant powder, dry extract, fixed combination, purified andrographolide, or a new delivery system. Then establish the exact chemical marker and its proportion, daily dose, and duration; otherwise two studies may describe non-interchangeable interventions. Next consider the population and primary outcome: adults with uncomplicated cold symptoms, people with pharyngotonsillitis, school prevention, and laboratory models are different clinical settings.

In the current evidence base, the most defensible area of study is short-term relief of some symptoms in uncomplicated ARI with certain specific products. Individual randomized trials differ in formulation, assessment time, and symptom scales; in the 2023 AP-Bio trial, the difference in the primary symptom measure appeared on day 3 but not days 5 or 7. These trials do not show that andrographis prevents pneumonia, hospitalization, bacterial complications, or viral transmission. A change in cellular NF-κB does not turn a product into a clinical antiviral medicine.

Do not derive universal acute or seasonal doses, add piperine or quercetin to increase exposure, or assemble a “synergy” blend from mechanistic hypotheses. The regimens in the table compare research interventions; they are not individualized directions. Having been tested in a trial does not remove differences between batches, regulatory status, or contraindications.

For comparison with other nutrients that have a separate evidence base and their own dose limits, see zinc and immune function. Evidence for one nutrient does not prove synergy with andrographis.

Method and limitations of this review

This is a narrative review of A. paniculata chemistry, signalling models, and clinical studies of respiratory symptoms. On 9 October 2026, the primary study of covalent modification of p50 Cys62, major RCTs of plant powder, Kan Jang and standardized AP-Bio/KalmCold extract, the small Bio-Immune study, and current TGA reports on anaphylaxis and its regulatory decision were checked specifically. Primary PubMed records were used for clinical numbers; the official TGA was used for Australian regulatory status. No formal systematic search, protocol-based risk-of-bias assessment, or GRADE evaluation was performed. Limitations include formulation and marker-dose variability, small or short RCTs, symptom rather than virologic or severe clinical outcomes, incomplete measurement of rare-event safety, and no confirmed human p50 Cys62 binding after product use.

Conclusion

Andrographolide is a chemically defined, reactive diterpenoid for which covalent interaction with p50 Cys62 and reduced NF-κB DNA binding have been described in preclinical models. Some specific extracts and combination products have been studied for ARI symptoms, but their composition, doses, participants, and assessment times differed; some improvements appeared only at a particular time point. This evidence does not establish efficacy of the purified compound, infection prevention, or treatment of severe viral disease. In evaluating a product, allergy safety and precise standardization matter at least as much as proposed anti-inflammatory activity.