Bitter Candytuft

Iberis amara L. was named by Linnaeus in Species Plantarum in 1753 and is the accepted name in Kew’s Plants of the World Online (POWO), which places it in Brassicaceae, the mustard and cabbage family, and gives its native range as western Europe to north-western Italy: Belgium, France, Germany, Great Britain, Italy, Spain, and Switzerland. The World Flora Online, drawing on the same Kew checklist, lists it as introduced in parts of eastern Europe, Asia, North and South America, and New Zealand, and Flora Mesoamericana describes it as cultivated and occasionally naturalized worldwide. Gerhard Madaus’s German textbook of 1938 gives the older synonyms Thlaspi amarum Crantz, Biauricula amara Bubani, and Crucifera iberis Krause. English names include wild candytuft, the name used by the Botanical Society of Britain and Ireland (BSBI), annual or rocket candytuft, clown’s mustard, and sciatica cress, while German has Bittere Schleifenblume and Bauernsenf, farmer’s mustard. The German herbal-medicine association Kooperation Phytopharmaka explains that Schleifenblume, bow flower, refers to the unequal petals, two small ones side by side and two large ones opposite, which suggest a ribbon bow. The garden annual I. umbellata and the evergreen perennial I. sempervirens are separate species, and BSBI notes that I. umbellata leaves lack the bitter taste.

It is an upright annual, rarely biennial, up to about 40 cm tall. BSBI’s species account by Peter Stroh describes more or less hairless leaves that widen toward a blunt tip, up to 6 cm long with two to four tooth-like lobes on each side, and very bitter to taste. The stems branch above into a crowded, flat-topped cluster of flowers that lengthens as the fruits form. The outer flowers of each cluster are much larger than the inner ones, and each flower is lopsided, with two large outer petals, white or sometimes lilac, and two much smaller inner ones. Busch and colleagues (BMC Plant Biology 2014) note that most of the mustard family has symmetrical flowers and only six genera have this one-sided form, and they linked the small inner petals of I. amara to stronger activity of a gene called IaTCP1. The fruits are flat, nearly circular pods 4–6 mm across, narrowly winged, notched at the tip, and topped by a persistent style. BSBI reports that the plant is largely self-incompatible and relies on insects for cross-pollination, flowers from May to as late as November depending on when the seed germinated, ripens its fruit about six weeks after pollination, and then dies.

In Britain, BSBI describes wild candytuft as an early colonist of bare chalk kept open by rabbits, grazing, frost, or ploughing, on warm south-facing banks, tracks, old chalk pits, and arable field edges, with a native range centered on the chalk of southern central England. It is listed as Vulnerable on the Great Britain Red List and has declined substantially since 1970, as myxomatosis cut rabbit numbers and downland was ploughed or became overgrown. Its bitterness is a defense: BSBI notes that rabbits find it unpalatable, and Huang and colleagues (Journal of Chemical Ecology 1993) found that its cucurbitacin glucosides deter the small white butterfly (Pieris rapae) from laying eggs on it. Madaus recorded it in fields and vineyards of south-western and western Germany, favoring limestone and dolomite. The medicinal raw material differs from older traditions, which used the seeds. For STW 5, the fresh or frozen whole plant, above-ground and underground parts together, is harvested between the start of flowering and full bloom; the Kooperation Phytopharmaka says the commercial supply comes from cultivated plants and that quality standards for the fresh plant (Iberis amara recens) are set in the German Drug Codex (DAC). Reichling and Saller (2002) specify the whole, blooming fresh plant with clear seed formation.

Bitter candytuft’s early history is tangled with that of cress. Madaus’s Lehrbuch der Biologischen Heilmittel (1938) relates that Galen explained the name iberis by a physician who cured a friend with the plant in Iberia, and that Pliny reported a book by Servilius Damocrates praising iberis after it healed a fellow physician’s lung complaint. Dioscorides recommended the root as a poultice for sciatica. Madaus adds, however, that Galen and many later writers treated iberis and lepidion, garden cress (Lepidium sativum), as the same plant until the sixteenth-century botanists Anguillara and Dodoens showed that they differed, so it is uncertain which plant the ancient authors meant. Later European writers clearly used Iberis on the skin. Madaus cites Matthiolus’s herbal of 1626, which recommended it externally for gout and sciatica because it reddens and blisters the skin. John Hill’s Family Herbal (1812), under the name sciatica cress, advised beating the leaves with a little lard and applying them for sciatica, or hip-gout, repeated as they dried, and called it ‘an approved remedy’ that was strangely neglected. The Dispensatory of the United States (1918) summed up that the plant appears to have been employed by the ancients in rheumatism, gout, and other diseases.

In the nineteenth century the seeds gained a reputation as a heart remedy. The 1918 Dispensatory reported that the seeds were considered the most effective part, that large doses were said to cause giddiness, nausea, and diarrhea, and that doses of one to three grains (0.065–0.2 g) of seed were said to be useful in cardiac hypertrophy, asthma, and bronchitis. Finley Ellingwood’s American Materia Medica (1919), written for Eclectic physicians, claimed that its most direct action was on an enlarged, functionally weak heart, recommended a tincture at five drops, named a bitter principle called lepiden as its constituent, and remarked that the agent had not received the attention it was said to deserve. Homeopaths adopted it for the same purpose: William Boericke’s materia medica (1901) credited the tincture with ‘great efficacy in cardiac diseases,’ listing palpitation, an irregular pulse, and cardiac breathlessness. Madaus recorded that the German Homeopathic Pharmacopoeia (HAB) prepared the tincture from the seeds, that rubs with the tincture or fresh-plant packs on the breastbone were used for angina pectoris, and that internal homeopathic use was rare and of doubtful success. None of these heart claims has been tested in modern trials.

The plant’s modern career is the story of STW 5. Annaházi and colleagues (Neurogastroenterology and Motility 2026) write that the nine-herb product, now Iberogast Classic, has been used clinically for upper digestive disorders for over six decades. It is made by Steigerwald Arzneimittelwerk in Darmstadt, marketed by Bayer Vital, and holds German authorization number 6463148.00.00, and laboratory papers from the 2000s code its bitter candytuft extract as STW 6. The six-herb STW 5-II was tested as a research preparation from about 2001 and has been sold as Iberogast N and as Iberogast Advance. Regulators have never reviewed bitter candytuft by itself: the Kooperation Phytopharmaka notes that neither EMA’s herbal committee nor the European Scientific Cooperative on Phytotherapy (ESCOP) has assessed it and that it has not been registered as a traditional herbal medicinal product, and in EU safety procedures it appears only as one of the extracts in Iberogast. Regulatory attention has centered on greater celandine instead. BfArM restricted oral celandine medicines in 2008; Bayer, which had contested the liver warnings in court, added them to Iberogast in 2018; and in 2021 EMA’s Pharmacovigilance Risk Assessment Committee (PRAC) asked for liver warnings on the product across the EU.

Bitter candytuft’s chemistry combines two defense systems. The Kooperation Phytopharmaka lists glucosinolates (mustard oil glycosides), bitter cucurbitacins, flavonols, amines, and, in the seeds, fatty oil. Glucosinolates are sulfur compounds that release pungent mustard oils when the plant is damaged, the source of the bite in mustard and cress. Huang and colleagues found sinigrin to be the most abundant glucosinolate in their plants and glucoiberin, named after the genus, a minor one; Jaki and colleagues (Journal of Natural Products 2002) characterized glucoiberin from I. amara as a reference standard and called it a prototype lead constituent. Cucurbitacins are intensely bitter, highly oxygenated triterpenes best known from bitter gourds and squashes. Gmelin isolated cucurbitacins J and K from the plant in 1963, and Huang’s group identified glucosides of cucurbitacins I and E as the compounds that deter egg-laying small whites. Dong and colleagues (Molecular Biology and Evolution 2021) identified the plant’s own enzymes for making them, including a cucurbitadienol synthase and two cytochrome P450 enzymes, and concluded that cucurbitacin production evolved independently in Iberis and in the gourd family. The fresh-plant extract also contains flavonoids, including a kaempferol glycoside first described from it by Kroll and colleagues (Die Pharmazie 2009). Madaus noted in 1938 that the homeopathic tincture contained little mustard oil unless the plant material was first left to ferment with myrosinase, the plant enzyme that releases it.

In laboratory tissue, bitter candytuft behaves differently from most of its partners in STW 5. Ammon and colleagues (Phytomedicine 2006) found that peppermint, chamomile, and licorice extracts relaxed strips of guinea pig small intestine contracted with acetylcholine or histamine, while the Iberis extract did not; instead it raised the resting tone of the muscle and made slack, atonic segments contract. STW 5 as a whole relaxed contracted segments and toned up relaxed ones, which the authors called a dual action and proposed as one reason the product might help both cramping and sluggish symptoms. In strips of guinea pig stomach, Schemann and colleagues (Phytomedicine 2006) found that STW 5 relaxed the upper stomach but stimulated the lower stomach, or antrum; bitter candytuft extract increased muscle activity in both regions, while angelica, chamomile, and licorice supplied the relaxing effect in the upper stomach. In mouse intestine, Sibaev and colleagues (Phytomedicine 2006) found that bitter candytuft increased the frequency and size of the electrical slow waves that pace contractions, while angelica and chamomile blocked them. These are animal tissue experiments at concentrations chosen by the investigators, and none shows what happens in a human gut after a 20-drop dose.

Other experiments point in several directions. In rats, extracts of bitter candytuft and each of the other STW 5 herbs reduced stomach ulcers caused by indometacin, lowered acid output, and raised mucus and prostaglandin E2, with the combined formulas working best (Khayyal and colleagues, Arzneimittel-Forschung 2001). In test-tube reactions, the Iberis extract, coded STW 6, scavenged reactive oxygen species and slowed fat oxidation (Schempp and colleagues, Arzneimittel-Forschung 2003). In rats with experimental arthritis, an Iberis extract reduced paw swelling and inflammatory messengers such as tumor necrosis factor-α and interleukin-1β (Khayyal and colleagues, Planta Medica 2015), and Weidner and colleagues (PLOS One 2016) found that it slowed the growth of colon cancer cells in culture and of human colon tumors grafted into mice. Not every result flatters the herb. In human esophageal cells, Ulrich-Merzenich and colleagues (Phytomedicine 2019) found that the bitter candytuft extract strongly stimulated release of interleukin-8, an inflammatory signal, whereas STW 5 as a whole suppressed it, an effect they credited to the other ingredients. None of these findings has been tested in people, and the arthritis and cancer results in particular are not reasons to take the herb.

Bitter candytuft has no established use on its own. The only controlled human data come from two trials of the Iberogast family. In the IBS trial by Madisch, Holtmann, Plein, and Hotz (Alimentary Pharmacology and Therapeutics 2004), 53 of the 208 patients took a bitter candytuft single-herb extract for four weeks, and their abdominal pain and IBS symptom scores did not differ significantly from those of the 52 on placebo (p = 0.15 and p = 0.12), while both combination products did. A 2002 German profile by Reichling and Saller described clear differences from placebo in IBS patients with diarrhea or alternating bowel habits, but the full published trial did not show an overall benefit. The other clue is indirect. In a 60-patient functional dyspepsia trial, Madisch and colleagues (Zeitschrift für Gastroenterologie 2001) compared STW 5, a research version without bitter candytuft, and placebo for four weeks; both herbal versions beat placebo, but a solid improvement came sooner with the complete formula (p = 0.023), and the authors concluded that bitter candytuft appeared to have an additive effect. With about 20 patients per group, that is a hint rather than proof. The Kooperation Phytopharmaka states that the efficacy and side effects of the fresh plant used alone are not sufficiently documented and that such use is therefore not recommended.

Functional dyspepsia is where STW 5 has the most data. In Melzer and colleagues’ 2004 meta-analysis, six randomized trials were identified, and the raw data of three placebo-controlled trials were pooled: the drops eased the most bothersome symptom more than placebo (odds ratio 0.22, 95% confidence interval 0.11–0.47), and a fourth trial found no significant difference between STW 5 and the prokinetic drug cisapride. Von Arnim and colleagues (American Journal of Gastroenterology 2007) then treated 315 patients with 20 drops three times a day or placebo for eight weeks; a validated gastrointestinal symptom score improved by 6.9 points with STW 5 and 5.9 with placebo, which the authors reported as evidence of efficacy. In the cisapride trial by Rösch and colleagues (2002), 186 patients were randomized, and both STW 5 and STW 5-II met the test for non-inferiority to the drug over four weeks. Cochrane’s 2023 review of non-Chinese herbal medicines (Báez and colleagues) found that STW 5 may moderately improve global symptoms over 28 to 56 days (mean difference −2.64 points; five trials, 814 participants) but rated the evidence very low certainty because of large differences between trials, rated a possible increase in the improvement rate as low certainty, and found that it may provide little or no benefit over other treatments.

The six-herb Iberogast Advance (STW 5-II) has its own trials. Madisch and colleagues (Digestion 2004) randomized 120 people with functional dyspepsia and found a significantly greater fall in symptom scores than with placebo during the first four weeks. In the largest trial, Vinson and colleagues (JGH Open 2024) gave 272 patients STW 5-II or placebo for eight weeks: 61.2% responded on the herbal product versus 45.1% on placebo (p = 0.008), although the average symptom score improvement narrowly missed significance (7.9 versus 6.7 points, p = 0.07). Andresen and colleagues (Digestion 2024) found four randomized trials with 613 patients, pooled the two suitable for an individual-patient analysis, and reported improvements in total symptoms and in fullness, early satiety, and upper abdominal pain at four and eight weeks, with no difference in treatment-related or severe side effects. The Storr and colleagues guideline from the German Society for Neurogastroenterology and Motility (2026) counts STW 5, STW 5-II, and peppermint oil with caraway oil as first-line options for functional dyspepsia, while describing the evidence as coming from various small randomized trials, mostly from German-speaking countries. The Cochrane authors, for their part, concluded that more high-quality trials of herbal medicines are needed, especially in people with common gut conditions occurring together.

For IBS, the same 2004 trial by Madisch and colleagues is the main evidence. After a standardized diagnostic work-up, 208 patients were randomly assigned to STW 5 (51), STW 5-II (52), the bitter candytuft extract (53), or placebo (52), and 203 completed four weeks. Both combinations reduced total abdominal pain scores and IBS symptom scores significantly more than placebo, while the candytuft extract did not. Bayer’s leaflet for Iberogast Advance states that its efficacy and tolerability were shown in one IBS trial lasting four weeks and one functional dyspepsia trial lasting eight weeks, and that repeat courses after symptoms return and long-term treatment have not been studied. In Germany, Iberogast Classic is licensed for functional and motility-related stomach and bowel disorders such as functional dyspepsia and IBS and as supportive treatment of gastritis symptoms, and Advance for functional dyspepsia and IBS. None of this tells us what bitter candytuft does by itself; where the herb was isolated, it failed, and where it was removed, the small difference favored keeping it.

Bitter candytuft reaches people almost entirely as Iberogast drops. Bayer’s mandatory product text gives the composition per 100 ml. Both versions contain 15.0 ml of an extract of fresh whole bitter candytuft plant (drug-to-extract ratio 1:1.5–2.5, made with 50% ethanol). Iberogast Classic adds extracts, all made with 30% ethanol, of chamomile flower (20.0 ml), angelica root, caraway fruit, milk thistle fruit, lemon balm leaf, greater celandine herb, and licorice root (10.0 ml each), and peppermint leaf (5.0 ml). Iberogast Advance adds chamomile flower (30.0 ml), caraway fruit (20.0 ml), lemon balm leaf (15.0 ml), peppermint leaf (10.0 ml), and licorice root (10.0 ml). Annaházi and colleagues describe the result as about 31% alcohol, and both leaflets state that each 20-drop dose contains 240 mg of ethanol, which they compare with less than 7 ml of beer or 3 ml of wine. The Kooperation Phytopharmaka mentions 50% hydroalcoholic extracts of the fresh plant as drops or in combinations, but gives no dose for the single herb, and no single-herb product has been tested in a trial.

The labeled doses differ slightly. For Iberogast Classic, the leaflet advises 20 drops three times a day for adults and adolescents from 13, 15 drops for children aged 6 to 12, and 10 drops for children aged 3 to 5, taken before or with meals in a little liquid, and sets no fixed limit on how long it can be used. For Iberogast Advance, adults and adolescents from 12 take 20 drops three times a day before or with meals in a little liquid, preferably water, and it is not recommended under 12. Both bottles should be shaken before use and held at a 45-degree angle when counting drops. Both leaflets ask people taking the product for the first time to see a doctor if symptoms have not improved after one week, to rule out an underlying disease, and to see a doctor whenever symptoms worsen or new ones appear. Opened bottles keep for four to eight weeks depending on size, as printed on the leaflet.

Practical points: check which Iberogast you have, because the two versions look similar; the leaflets describe a green cap for Classic and a purple cap for Advance, and only Classic contains greater celandine and carries liver warnings. Do not make your own bitter candytuft tea or tincture. There is no tested dose, the plant’s cucurbitacins are toxic, and the Kooperation Phytopharmaka notes that the finished products are dosed so that no significant amounts of cucurbitacins pass through the gut wall, which cannot be assumed for a homemade preparation. Homeopathic Iberis preparations, traditionally made from the seeds, are a different product with no evidence for heart or digestive use. Wild plants should be left alone as well: wild candytuft is Vulnerable in Great Britain, and BSBI notes that it can be confused with garden candytufts that escape into the wild. Products sold outside Germany under similar names may differ, so read the ingredient list.