Benefits
Soothing film for the mouth and throat in EU traditional use
Iceland moss is registered in the EU as a traditional herbal medicine used as a demulcent for an irritated mouth or throat and the dry cough that can come with it. That status rests on at least 30 years of documented use. The regulator found no placebo-controlled trials, and the clinical reports it reviewed were small and had no placebo group.
Mouth and throat dryness after nasal surgery in a lozenge dose study
In 61 adults breathing only through the mouth after nasal surgery, lozenges equal to 0.48, 3 or 5 g of dried lichen a day (strengths as given by EU regulators) were compared for 5 days. Dryness, coating and inflammation improved in all three groups with no difference between doses. There was no placebo group, so natural recovery after surgery cannot be ruled out.
Lozenge tolerability in children aged 4 to 12
In a post-marketing survey of 3,143 children with upper airway complaints who sucked Iceland moss lozenges for 1 to 2 weeks, possible reactions occurred in 6 children (0.2 percent): itching, nausea, stomach upset or mouth burning, all passing on their own. Most children were rated recovered or improved by the end, but with no control group this cannot be credited to the lozenges.
Traditional bitter used to support appetite
EU regulators also accept Iceland moss tea for temporary loss of appetite in adults, based on its use as a bitter. They found no clinical or laboratory studies of this use and judged it plausible only because the lichen acids taste bitter. Persistent loss of appetite needs a medical check.
Lichenan gel that resembles a saliva mucin in lab tests
In a laboratory comparison of plant gels as possible saliva substitutes, lichenan from Iceland moss came closest to the main salivary mucin and, once buffered, clung to human cheek cells about as firmly as natural saliva. In an older pig cheek tissue test, as summarized by EU regulators, its polysaccharides adhered only slightly. Neither was a study in people.
Immune cell signaling in cell and rat studies
In human immune cells grown in a dish, a water extract raised both IL-10, an anti-inflammatory messenger, and IL-12, with IL-10 rising more, an effect traced to lichenan. Injected under the skin of rats, the extract reduced induced arthritis, at the highest of three doses only according to an EU review. Neither result shows an effect from swallowing Iceland moss.
Mechanism of action
Swelling polysaccharides coat the mouth and throat
Lichenan, a hot water soluble beta-glucan, and isolichenan, a cold water soluble alpha-glucan, make up much of the dried lichen and swell into a viscous mucilage. Sucked slowly as a lozenge or sipped as tea, it is thought to form a protective film on the lining of the mouth and throat. How long that film lasts has not been measured in people.
Bitter lichen acids behind the appetite tradition
Fumarprotocetraric acid (about 2.6 to 11.5 percent) and protolichesterinic acid (about 0.1 to 1.5 percent) give the lichen its bitterness, the basis for its use as a bitter. They dissolve poorly in cold water. In a simulated digestion model, protolichesterinic and related paraconic acids stayed stable, and they acted as antioxidants in intestinal cells in a dish.
Lichenan shifts immune cell messengers in vitro
In human dendritic cells, lichenan reproduced the extract's rise in IL-10 relative to IL-12, while isolichenan and the lichen acids were inactive. This is a cell culture effect at set concentrations; whether any lichenan reaches immune tissue after swallowing is unknown.
Clinical trials
Randomized comparison of three concentrations of Iceland moss extract lozenges (Isla-Moos), given from the first to the fifth day after nasal septum surgery; the EMA review describes it as double-blind with no placebo arm. Article in German with an English abstract. (Kempe et al. 1997, Laryngorhinootologie)
61 patients (63 in the EMA summary, aged 18 to 65) breathing through the mouth because of nasal packing after surgery on the nasal septum.
Mucosal coating, dryness and inflammation, tongue coating, hoarseness and sore throat improved in all groups, with no significant difference between lozenges equal to 0.48, 3 or 5 g of dried lichen a day (strengths from the EMA summary; the abstract states only the 0.48 g dose). The authors concluded the lowest dose (10 lozenges a day) was enough. With no placebo, the improvement cannot be separated from normal healing after surgery. No side effects were reported.
Multicenter post-marketing surveillance study in about 300 mainly pediatric practices in Germany of Isla-Moos (80 mg aqueous extract) and Isla-Mint (100 mg) lozenges; the first author's listed affiliation is the German drug company Engelhard Arzneimittel. Article in German with an English abstract. (Hecker et al. 2004, Forsch Komplementarmed Klass Naturheilkd)
3,143 children aged 4 to 12 with upper respiratory complaints (1,848 Isla-Moos, 1,295 Isla-Mint), treated for 1 to 2 weeks; 61 percent took 4 to 6 lozenges a day.
73 adverse events in 57 children (1.8 percent) were mostly attributed to the underlying illness. Seven events in 6 children (0.2 percent) were possibly related: itching twice, nausea twice, abdominal pain, heartburn and mouth burning, all resolving on their own. By the end, 39 percent were rated fully recovered and 55 percent improved, but with no control group these symptom figures do not show efficacy.
Laboratory study of a traditionally prepared water extract and purified compounds (lichenan, isolichenan, protolichesterinic and fumarprotocetraric acids), plus a rat model of induced arthritis. No human participants. (Freysdottir et al. 2008, Int Immunopharmacol)
Human monocyte-derived dendritic cells in culture, and rats with antigen-induced arthritis given the extract by injection under the skin.
The extract raised secretion of both IL-10 and IL-12p40, with IL-10 more prominent; lichenan did the same, while isolichenan and the lichen acids were inactive. Rats given the extract developed significantly less arthritis than saline-treated rats (according to the EMA summary, only at the highest of three doses). The extract was injected, not swallowed.
Laboratory study comparing water extracts of calendula, Fucus seaweed and lichenan from Iceland moss as candidate saliva substitutes, including a new adhesion test with human buccal cells. No human participants. (Winter et al. 2024, Pharmaceutics)
Plant polysaccharide preparations tested against human saliva and human buccal epithelial cells.
Lichenan was the best candidate to mimic the salivary mucin MUC5B. After its pH, osmolality and buffering were adjusted, it showed high cell adhesion, with a maximum detachment force comparable to unstimulated whole mouth saliva. This supports the idea of a mucilage film but does not show relief of dry mouth in people.
Animal feeding study of traditional emergency foods in Finland, including Iceland moss given untreated or after the traditional wood ash soaking and boiling. No human participants. (Airaksinen et al. 1986, J Ethnopharmacol)
Mice fed diets of 50 percent plant material, and rats fed 25 percent ash-treated Iceland moss for 3 months.
No 50 percent mixture was tolerated by mice. Rats tolerated 25 percent ash-treated lichen rather well but gained less weight, and at the end had protein in the urine and kidney tubule changes, which the authors linked to high lead levels in the lichen and in the rats' kidneys. These are food-scale amounts, far above supplement doses.
Laboratory analysis of 14 samples of cut, dried Iceland moss bought from different suppliers on the European market, measuring trace elements in the raw lichen and in the decoction made from it. No human participants. (Giordani et al. 2017, Chemosphere)
14 commercial samples of dried Iceland moss and their decoctions.
Arsenic, cadmium, lead, nickel and other elements were measured. Levels in the decoctions were significantly lower than in the raw lichen, down to levels of negligible health concern, and differences between suppliers seen in the raw material disappeared in the teas. Transfer from lichen to tea ranged from 2 percent for copper to 95 percent for zinc.