Is elderberry actually medicinal? What the clinical trials say

Elderberry is one of the most talked-about plants in the natural health world. Syrup, tinctures, capsules, gummies — the elderberry supplement industry is enormous. The claims are correspondingly bold: “boosts immunity,” “fights the flu,” “antiviral powerhouse,” “nature’s medicine chest.” Some of those claims have genuine research behind them. Others are marketing copy dressed up as science. And a few of the fears circulating about elderberry — particularly the cytokine storm concern — are not well-supported by evidence either.

Today is Saturday, which means myth-busting day. Elderberries (Sambucus nigra) are not yet in season in the UK — they ripen in late August through September — but now is exactly the right time to understand what the research actually says, so that when September arrives you can use them with genuine confidence. What follows is an honest, PubMed-grounded look at what the clinical trials have found, what the limitations are, what the real safety concern is (not the one you’ve probably heard about), and how to make the most effective use of the plant.

What is elderberry, and when does it appear in the UK?

Elder (Sambucus nigra) is a fast-growing hedgerow and woodland tree, one of the most common in Britain. It is easy to identify by its deeply furrowed grey-brown bark, its opposite pinnate leaves with 5–7 sharply toothed leaflets, its large flat-topped clusters of tiny creamy-white flowers in June and July (elderflowers), and its heavy, pendulous clusters of small, round, deep purple-black berries in late August through October. The wine-red berry stems — darker than the green leaf stems — and the characteristically musty smell of the crushed leaves are useful additional identifiers.

UK seasonal availability: Elderflowers: June–July. Elderberries: late August–October, depending on location and year. Both parts of the plant are used — this post focuses on the berries, which have the most clinical research behind them. For elderflower, the flavour and culinary uses are quite different, though some of the bioactive compounds overlap.

⚠️ Identification note: The main lookalike risk with elder is Sambucus ebulus — dwarf elder or danewort — which produces similar-looking berries but is toxic. Dwarf elder is a herbaceous plant (dies back in winter, no woody stem), rarely grows taller than about 1.5m, has a rank unpleasant smell, and its flowers are more pink-tinged than the creamy white of S. nigra. True elder is a tree or large shrub with clearly woody stems. If in any doubt about which elder species you have found, do not use the berries. Never eat any wild plant unless you are 100% confident in your identification.

The real safety issue: raw elderberries are toxic

Before we get to the clinical evidence for elderberry’s benefits, let’s address the safety issue that is sometimes overlooked in the rush to celebrate its medicinal properties: raw elderberries contain cyanogenic glycosides — primarily sambunigrin — which can cause nausea, vomiting, and diarrhoea if consumed raw in any meaningful quantity. This is documented in the phytochemistry literature (PMC8156197), and reports of gastrointestinal illness following consumption of raw or unripe elderberries are well established.

The good news: heat destroys the cyanogenic glycosides. Cooking elderberries — even briefly, as in making a syrup, jam, or cordial — renders them safe. The concentration of these glycosides is highest in unripe berries, seeds, bark, and leaves; lowest in ripe cooked fruit. A 2021 analysis (PMC7961730) confirmed that standard food preparation methods are effective at eliminating the cyanogenic glycoside risk. The practical rule is simple and non-negotiable: always cook elderberries before consuming them. This applies to any preparation, including syrups, tinctures made with heat, and cooked jams. Do not eat them raw off the plant.

What does the clinical evidence actually show?

This is where elderberry genuinely earns its reputation — and where it’s important to be precise about what the evidence shows and what it does not.

The clinical trial evidence for upper respiratory illness

The most robust evidence comes from a 2019 meta-analysis published in Complementary Medicine Research (Hawkins et al., PMID: 30670267) which pooled data from randomised controlled trials examining the effect of black elderberry supplementation on upper respiratory symptoms. The meta-analysis found that elderberry supplementation substantially reduced the overall duration of upper respiratory symptoms — in cold sufferers, by an average of around two days, and the effects on symptom severity were also significant. This is a meaningful clinical effect.

Two earlier landmark RCTs support this finding. A 2004 randomised, double-blind, placebo-controlled trial (Zakay-Rones et al., Journal of International Medical Research, PMID: 15080016) found that patients given elderberry extract during influenza recovered on average 4 days faster than the placebo group (3–4 days vs 7–8 days). A 2001 RCT from the same research group (PMID: 11399518) found that Sambucol elderberry extract reduced flu duration significantly in a double-blind placebo-controlled design and that convalescent serum from the elderberry group showed markedly higher antibody titres against influenza strains. These are not in vitro studies or animal studies — these are human clinical trials.

Important caveat: most of these trials used standardised commercial extracts (primarily Sambucol®) — not fresh foraged berries or homemade syrup. The concentration of active compounds, particularly the anthocyanins cyanidin-3-glucoside and cyanidin-3-sambubioside, may differ significantly between a standardised pharmaceutical-grade extract and a home preparation. The clinical results cannot be assumed to transfer directly to homemade syrup, though well-made preparations using ripe, fully cooked berries are likely to contain meaningful anthocyanin levels.

How does it work? The proposed mechanisms

The primary bioactive compounds in elderberry fruit are anthocyanins — particularly cyanidin-3-sambubioside and cyanidin-3-glucoside. These give the berries their deep purple-black colour and appear to drive much of the antiviral activity. In vitro studies have shown that these compounds can inhibit the binding of influenza virus to host cell receptors — effectively blocking viral entry — and may also interfere with viral replication. A 2009 study (PMID: 18040528) established that elderberry anthocyanins are absorbed and excreted in humans, confirming bioavailability, though levels are relatively low and variable.

Elderberries also contain flavonoids (quercetin, rutin, kaempferol), phenolic acids, and meaningful amounts of vitamin C. The quercetin content is relevant — as we explored in Wednesday’s post on quercetin and the hedgerow, this flavonoid has its own anti-inflammatory and antiviral properties supported by clinical trial data.

The cytokine storm myth: what the evidence actually says

During the COVID-19 pandemic, a concern circulated widely that elderberry could stimulate an excessive immune response — a “cytokine storm” — and should therefore be avoided, particularly by vulnerable people. This concern was repeated across social media and even in some medical settings. It is worth examining carefully, because the evidence does not support it.

A 2021 systematic review in Advances in Integrative Medicine (PMID: 33827515; also PMC8026097) specifically examined this concern and reviewed eight clinical studies on elderberry use. The conclusion was clear: “there is no evidence that elderberry overstimulates the immune system.” A 2022 review in Advanced Biomedical Research (PMC9744084) also addressed this directly, acknowledging the theoretical concern while noting that “there is not yet enough evidence to support or refute this claim” — and that the available human clinical data does not show immune overstimulation in practice. The concern originated from in vitro observations of cytokine-stimulating effects in isolated immune cells, which do not straightforwardly translate to whole-body immune responses in humans.

This does not mean elderberry is risk-free for everyone — people on immunosuppressant medications or with autoimmune conditions should always consult their GP before using medicinal plant preparations. But the cytokine storm framing, which was presented as settled science in many popular health spaces, is not supported by the clinical literature.

The honest verdict: what elderberry can and cannot do

Based on the current evidence, here is an honest evidence-graded summary:

• Likely effective (human RCT evidence): Reducing duration and severity of upper respiratory symptoms — colds and flu. The meta-analysis and individual RCT evidence is genuine and meaningful. This is not “immune boosting” in a vague marketing sense; it is a measurable effect on symptom duration in clinical trials.
• Preliminary evidence (in vitro / mechanistic): Direct antiviral activity via inhibition of viral binding to host cells. Plausible mechanism, needs more human clinical confirmation.
• Nutritional contribution (established): Meaningful anthocyanin, quercetin, vitamin C, and fibre content. Elderberries eaten as food — in jams, syrups, cordials — are nutritionally valuable independently of any medicinal claim.
• Not supported by evidence: Causing cytokine storms in otherwise healthy people. The concern is theoretical and not borne out in clinical studies.
• Genuine risk requiring action: Raw elderberries contain cyanogenic glycosides. Always cook before consuming.

How to make elderberry syrup: the method that preserves the most

The standard approach — simmer with a little water and spices, strain, then add honey off the heat — is well-suited to preserving anthocyanin content while ensuring full destruction of sambunigrin. Adding honey after removing from the heat matters: prolonged heating degrades honey’s own antimicrobial compounds. Adding a small amount of vitamin C (from lemon juice) may help stabilise the anthocyanins.

Basic elderberry syrup

• 500g ripe elderberries, stripped from stems with a fork (discard all stems — they contain higher glycoside levels)
• 300ml water
• 1 cinnamon stick
• 3 cloves
• 1 teaspoon fresh grated ginger
• Juice of half a lemon
• 3–4 tablespoons raw honey (added off the heat)

Combine elderberries, water, and spices in a saucepan. Bring to a simmer and cook gently for 20–25 minutes until reduced by roughly one third. Remove from the heat. Allow to cool slightly (not fully — still warm but not boiling). Strain through a fine sieve or muslin, pressing the berries to extract all the liquid. Stir in the lemon juice and honey. Pour into sterilised dark glass bottles. Store in the fridge; use within 3–4 weeks. A tablespoon daily, or more frequently at the onset of respiratory symptoms, is the dose used in most of the clinical studies.

Note on preparation: Do not use an aluminium pan — elderberry juice reacts with aluminium. Use stainless steel, enamel, or cast iron. Do not drink the juice of raw uncooked berries. Ensure all berries are fully ripe (deep purple-black, not red) before using.

When to start preparing: what to look for this autumn

Elder trees are flowering right now across the UK — those flat-topped creamy-white flower clusters are the best possible way to locate your autumn harvest. Mark the trees you find this June and July; return to the same spots in late August to early September. The berries are ripe when the entire cluster is deep purple-black with no remaining red berries, and when they hang heavy and pendulous on the wine-red stems. Taste one raw (a single berry is unlikely to cause more than a slightly unpleasant flavour; do not eat a handful) — ripe elderberries have a deep, astringent, earthy taste, quite unlike the sweetness of blackberries. If in doubt about ripeness, wait another week.

If you’d like to learn to identify elder and other medicinal hedgerow plants with confidence in the field, I run foraging workshops throughout the year — including late summer sessions specifically focused on the elderberry, rosehip, sloe, and hawthorn berry harvest. And if you’re interested in how wild plant compounds like elderberry anthocyanins and quercetin fit into the broader science of cellular health and biological ageing, that’s exactly the territory we explore in The Cellular Reset programme.

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References
Hawkins, J. et al. (2019). Black elderberry supplementation effectively treats upper respiratory symptoms: a meta-analysis of randomized controlled clinical trials. Complementary Medicine Research. PMID: 30670267
Zakay-Rones, Z. et al. (2004). Randomized study of the efficacy and safety of oral elderberry extract in the treatment of influenza A and B virus infections. Journal of International Medical Research. PMID: 15080016
Zakay-Rones, Z. et al. (2001). Inhibition of several strains of influenza virus in vitro and reduction of symptoms by an elderberry extract during an outbreak of influenza B. Journal of Alternative and Complementary Medicine. PMID: 11399518
Wieland, L.S. et al. (2021). Elderberry for prevention and treatment of viral respiratory illnesses: a systematic review. BMC Complementary Medicine and Therapies. PMID: 33827515
Nair, B. et al. (2022). The pros and cons of using elderberry for the prevention of COVID-19. Advanced Biomedical Research. PMC9744084
Senica, M. et al. (2021). Cyanogenic glycoside analysis in American elderberry. Molecules. PMC7961730

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This content is for educational purposes only and does not constitute medical advice. Wild plants can be dangerous if misidentified. Raw elderberries are toxic — always cook before consuming. Elderberry may interact with immunosuppressant medications. Never consume any wild plant unless you are completely confident in your identification. Always consult your GP before using wild plants medicinally, particularly if you are pregnant, breastfeeding, or taking medication.

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