Elderberry (Sambucus spp; S nigra is one of the more commonly used species in research) is a shrub, formerly classed in the Caprifoliaceae family but now recognized to be in the Adoxaceae. Species of Sambucus are known to grow on most continents, with the exception of Oceania and Antarctica. Both elderflowers and elderberries are consumed for food and traditional medical purposes.^[2] Since elderberry shrubs have become naturalized in so many locations, they have traditional uses across many cultures. Two of the more popular uses for elderberries have been in the prevention of flu or colds and in immune stimulation.^[14] The berries themselves are known to contain relatively high amounts of anti-inflammatory and antioxidant compounds such as anthocyanins and flavonols.^[15] Elderberries also contain nutrients such as B vitamins, ascorbic acid, folic acid, potassium, and fructose.^[16]

Current meta-analyses support elderberry’s use for the prevention and/or treatment of respiratory infections (mainly those caused by respiratory viruses, such as COVID-19 and influenza), and elderberry’s capacity to strengthen immune response under stressful circumstances, such as air travel, exercise, or exposure to extreme environments.^{[4][5][11][17][12]}

Clinical trials have also studied elderberry for cardiovascular disease,^[6][9] topical treatment of eczema,^[7] gingivitis prevention,^[8] lipid or carbohydrate oxidation,^[9][13] and influenza treatment.^[10]

Elderberry leaves, stems, and unripe or uncooked fruit contain a toxin, sambunagrin, which causes nausea, vomiting, and diarrhea, especially when taken in larger quantities.^[3] Because elderberry may act on the immune system, people who are immunocompromised or who have autoimmune conditions should not consume elderberry medicinally without a physician’s supervision.^[2] There have been case reports connecting consumption of elderberry extract with acute pancreatitis,^[18] processing of elderberries with repeat-exposure-induced allergies,^[19] and consumption of raw fruit, stems and leaves with symptoms consistent with poisoning (nausea, vomiting, dizziness, numbness, and stomach cramps).^[20]

So far, the best explanation for elderberry’s positive effects is related to the high polyphenol content, which is likely responsible for its anti-inflammatory or antioxidative benefits.^[16][15] More specifically, the primary flavonols found in elderberry, including rutin, isoquercitrin, and astragalin, likely provide antioxidant capacity,^[21] while elderberry anthocyanins such as cyanidin-3-O-glucoside are thought to play a role both in reducing inflammation and in defending against infection and malignancies.^[16][15] As with any herb or plant, the total content and composition of bioactive constituents may vary depending on the cultivar and on the conditions in which the plant was grown.^[16][15]