Elderberry

What it is

Black elder (Sambucus nigra) is a shrub whose dark berries have long been used for colds and respiratory problems [1]. Trials tested standardised extracts in capsules or syrup, not fresh berries [2][3].

What the research says

The strongest finding is for shorter colds. In a trial of 312 air travellers, the combined cold days were 57 on elderberry against 117 on placebo, although the number of colds did not differ significantly [2]. A 2019 meta-analysis of small trials, with 180 people, reported a substantial reduction in upper respiratory symptoms, without an effect size in its abstract [4]. A 2021 systematic review rated the benefit for colds and flu as uncertain, and found that elderberry may not prevent colds: 8% on elderberry against 11% on placebo, not significant [1].

For flu, two small trials from 1995 and 2004 (87 people) pooled to about 2.7 days sooner [1], and a 2004 trial reported symptoms eased about four days earlier [3]. A 2020 trial of 87 emergency room patients found no difference, with 4.9 days on placebo and 5.3 days on elderberry until symptoms were none or mild [5].

Doses used in studies

In the air-travel trial, people took a 300 mg extract capsule: two a day (600 mg) for about 10 days before travel, then three a day (900 mg) during travel and for about five days after arriving [2]. The 2004 flu trial used 15 ml of syrup four times a day for five days [3]. The 2020 flu trial used 15 ml of extract twice a day for children aged 5 to 12, and four times a day for those over 12, for five days [5]. These are doses used in trials, not recommendations.

Safety and interactions

Side effects: the 2021 review found no serious adverse events in the trials, but adverse-event reporting was inconsistent. In the prevention trial, there were 2 events in the placebo group and 3 in the elderberry group [1]. Upper limits: we found no upper intake limit in the studies read. Medicine interactions: we found no human study of interactions with blood thinners, diabetes or blood-pressure drugs, or immune-suppressing drugs. Pregnancy and breastfeeding: a 2014 review found no safety studies of elderberry in pregnancy and advised against its use for infections [6]. People with autoimmune disease were excluded from the air-travel trial [2]. Kidney and liver: we found no safety data for people with kidney or liver disease. Raw berries and stems: a lab analysis found cyanogenic compounds, which can release cyanide, mainly in stems and green berries; commercial juice had none that could be measured [7]. No human study has tested raw berries.

Caveats and open questions

The largest cold trial was funded by the maker of the extract it tested [2]. The flu results conflict: an older pooled result [1] against a 2020 trial with no difference [5]. The 2020 trial also ran an after-the-fact analysis that suggested elderberry taken alone did worse than placebo, which was not planned [5]. A 420-person trial (NCT05435144) is registered, but its status is listed as unknown, so no results were found.