Elderberry and the cytokine storm myth that wouldn't die

In March and April 2020, social media posts circulated warning that elderberry syrup could trigger a fatal "cytokine storm" in COVID-19 patients and recommending that elderberry products be discarded. The claim originated in a misreading of a 2001 in vitro paper and propagated despite repeated debunking by clinical herbalists, infectious-disease physicians, and the manufacturers themselves. Six years later the meme still recurs in flu seasons.

What the original 2001 paper actually showed

The Mumcuoglu group's 2001 publication in J Altern Complement Med showed that elderberry extract (Sambucol) increased production of several inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-8) and the anti-inflammatory cytokine IL-10 in cultured human monocytes (PMID: 11399518).¹ This was framed by the authors as evidence of immune activation, consistent with the proposed mechanism for elderberry's modest antiviral effect against influenza. The 2020 social-media claim translated "increased cytokines in cultured cells" into "causes cytokine storms in COVID patients," skipping every layer of intervening biology including bioavailability, route, dose, and in vivo regulation.

Why the leap to cytokine storm is biologically implausible

Cytokine release syndrome in COVID-19 and other infections involves systemic IL-6 levels often exceeding 100 pg/mL, accompanied by ferritin, D-dimer, and CRP markers and clinical haemodynamic instability. Oral elderberry extract produces nothing remotely close to this systemic profile. A 2021 pharmacologic analysis of elderberry anthocyanin bioavailability estimated peak plasma concentrations of cyanidin-3-glucoside at low nanomolar levels — orders of magnitude below the in vitro concentrations used in the Mumcuoglu cell-culture work (PMID: 33800942).² No case series or pharmacovigilance database has identified elderberry as a precipitant of cytokine release syndrome in humans, before or during COVID-19.

What elderberry actually does in human trials

The clinical evidence for elderberry in upper-respiratory illness is small but directionally positive. A 2004 RCT in 60 adults with influenza A/B showed shorter symptom duration with elderberry syrup versus placebo (PMID: 15080016).³ A 2016 RCT in 312 air travellers reported reduced upper-respiratory symptom severity with prophylactic elderberry capsules (PMID: 27023596).⁴ A 2019 meta-analysis pooled 4 RCTs (n=180) and reported a 2-day reduction in symptom duration; the trials were small and the certainty rating modest (PMID: 30670267).⁵ No elderberry RCT has tested COVID-19 specifically, and any extrapolation to SARS-CoV-2 is unsupported.

The legitimate elderberry safety considerations

Raw or unprocessed elderberry contains cyanogenic glycosides (sambunigrin) that produce nausea, vomiting, and diarrhoea. The 1983 California outbreak of acute gastrointestinal illness from raw elderberry juice highlighted this risk (CDC MMWR, 1984; PMID: 6700660).⁶ Commercially processed elderberry syrups, jams, and standardised extracts are heat-treated and effectively safe. Pregnant or lactating women have no clinical-trial data and should avoid concentrated extracts as a precaution. Patients on immunosuppressants have an unknown interaction profile, although no clinical interactions are documented.

Where the myth came from and why it persisted

The cytokine-storm framing was amplified by a March 2020 blog post that misinterpreted both the Mumcuoglu paper and the emerging COVID-19 immunopathology. The post was widely shared by influencers who were not virologists. Mainstream herbal medicine organisations and infectious-disease researchers responded within weeks, and the American Herbalists Guild issued a clarifying statement. By the time fact-checks caught up, elderberry's reputation had taken a hit it did not deserve (PMID: 33064236).⁷ A 2024 review in Microorganisms summarised the elderberry evidence base across influenza, common-cold, and the COVID-era speculation, concluding that the cytokine-storm hypothesis has no human clinical support (PMID: 39124312).⁸

The honest takeaway

Elderberry is one of the few herbal products with small but directional RCT evidence for modestly shortening influenza and cold symptoms when started within 48 hours of onset. It is not a cure, not a substitute for vaccination, and does not cause cytokine storms in humans at any oral dose used in trials or commerce. Raw elderberry should not be consumed without processing. Commercial standardised extracts at typical labelled doses are safe in adults.