Iceland moss (Cetraria islandica): Uses, Evidence and Safety

Safety first: a lichen that soaks up pollution

Iceland moss is a lichen, and lichens are very sensitive to air pollution and can take up toxic elements from the environment. [2] The EU assessment report describes high lead levels in some wild samples, plus radioactive substances such as caesium-137 that built up in the lichen after nuclear tests; after the Chernobyl accident it was hard to find Scandinavian material with low radioactivity, and the situation was said to have improved since 1994. [2] In animal tests, untreated lichen as half of the food was fatal to mice, and rats fed treated lichen for three months showed mild kidney changes that the researchers linked to lead. [2] These animal findings do not describe normal use of a tested medicine, and the EU reviewers concluded that no safety concern arises for the quality-controlled herbal substance, which has a lead limit in the European Pharmacopoeia. [2] Even so, wild-picked lichen or products without testing are a different matter. The EU says use in pregnancy and breastfeeding is not recommended because safety has not been established. [1] This page is information, not a recommendation. See heavy metals, pesticides and microbes in herbal products.

Overview

Iceland moss is the common name for the body (thallus) of the lichen Cetraria islandica. A lichen is a partnership between a fungus and an alga, so it is neither a moss nor a plant. [3][8] GBIF lists Cetraria islandica (L.) Ach. as the accepted name, in the family Parmeliaceae. [5] A herbal reference site (a secondary source) says it grows widely in cold northern and mountain regions, and that the commercial supply comes from wild collection, mainly in Scandinavia, the Balkans and Russia. [9] The part used is the whole dried thallus. It is a different organism from the lichen on our usnea page and from the seaweed on our Irish moss page. This page covers Iceland moss as a tea, extract, tincture and lozenge ingredient.

Traditional use (not proof of benefit)

In Europe, Iceland moss preparations have been used for a long time as a soothing agent (a "demulcent") for irritation of the mouth and throat with a dry cough, and for temporary loss of appetite. [1][3] The EU committee accepted both uses on the basis of long-standing use only. It said clinical trial evidence was not enough, and it considered the appetite use plausible because the lichen acids in it taste bitter. [3][2] A 2023 laboratory paper also lists tea or decoction for dry cough, appetite loss and mouth problems, and says it is used as a food ingredient in sweet dishes. [8] That paper also says Iceland moss is used for lung disease, mainly tuberculosis, but gives no data for this. [8]

What research shows

The research is small and old. The EU committee found no controlled clinical studies and called the human data insufficient for a "well-established use" ruling. [2]

Proper evidence not found in the sources we read for Iceland moss improving a cough, throat infection or appetite compared with placebo.

Forms and why the form matters

The EU monograph covers the chopped dried lichen for tea (an infusion or a cold-water soak), two types of water-based soft extract for use in the mouth (lozenge-type products), and an alcohol tincture. [1] The tea and soak forms carry mucilage (a gel-like fibre) that coats the mouth and throat, and the EU advises using the soak straight after it is made. [1][2] The monograph also notes that the tincture contains alcohol and must be labelled as such. [1] The EU report notes that the bitter lichen acids dissolve poorly in cold water, even though a cold soak is often recommended as an appetite aid in older reference books. [2] Combination products are not covered by the EU summary. [3] Amounts are for a pharmacist or clinician, not this page.

Safety in more detail

• Common side effects: none were known to the EU committee, and no overdose case or serious reaction was reported. [1][2] In a safety survey of 3,143 children aged 4 to 12 using lozenges, 6 children had reactions that could not be ruled out as caused by the lozenge, such as itching, nausea, a burning mouth or abdominal pain; all went away on their own. [2]
• Allergy: the EU contraindication is allergy to the lichen. [1] A 1980 patch-test study in people with light-sensitive skin found 8 positive reactions to Iceland moss, so contact allergy is possible in sensitive people. [2]
• Medicines: the monograph says no interactions have been reported, but taking it at least half an hour to an hour away from other medicines is advised as a precaution because the gel-like fibre might delay absorption. [1][2] A consumer drug reference makes a similar point and rates this as a moderate interaction. [10]
• Pregnancy and breastfeeding: not recommended because safety has not been established; tests on reproductive harm, genetic damage and cancer have not been done. [1] A consumer drug reference says it may be unsafe in pregnancy because of possible lead. [10] See pregnancy and breastfeeding safety.
• Children: the EU says the tea is not recommended under 12, the tincture and the appetite use not under 18, and mouth-dissolving extracts not under 6, because of a lack of data and the form. [1]
• Seeing a doctor: the EU says to get advice if symptoms last longer than a week, or if breathlessness, fever or pus-coloured phlegm appear. [1]
• Liver and kidney: no human liver warning was found for Iceland moss in the sources we read. Mild kidney changes in rats were linked to lead in the lichen. [2] We make no claim about people with kidney disease.
• Usnic acid question: usnic acid is the compound tied to serious liver injury in some weight-loss supplements. [7] The EU report found only traces (0.04% in one old analysis) or none in Iceland moss. [2] A 2023 laboratory study of one specimen from Kazakhstan did identify usnic acid among its isolated compounds, so content may vary by sample. [8] The EU report also notes that EFSA lists the lichen in its compendium of botanicals of possible concern, because of usnic-acid-type compounds and its tendency to collect heavy metals. [2] Proper evidence not found in the sources we read about liver injury from Iceland moss tea or lozenges.
• Quality and contamination: the EU report says medicine-grade material can be identified with certainty under a pharmacopoeia monograph, so adulteration is not expected for it. [2] Wild-collected or foraged lichen is not covered by that check. For product-testing advice see third-party testing for herbal products.
• Stomach ulcers: a consumer drug reference advises against use with stomach or small-intestine ulcers because it may irritate the lining; we did not find this in the EU documents. [10]

Official statements

• EMA (EU), monograph adopted 24 November 2014: a traditional herbal medicine for soothing mouth and throat irritation with dry cough, and for temporary loss of appetite (adults only); use in pregnancy and breastfeeding not recommended. [1]
• EMA, public summary dated 31 January 2017: the uses rest on long-standing use; clinical studies had few patients and no placebo group. [3]
• EMA product page: lists the assessment as finalised; an addendum was published on 8 March 2022 (we did not read it). [4]

Related pages

• Marshmallow root
• Slippery elm
• Mullein
• Herbs for colds, flu and cough: what research shows
• Herbal tea for sore throat, cough and colds
• Usnea