Althaea officinalis is a plant that contains several phytochemicals, including phytosterols, flavonoids, and polysaccharides.^{[1][2][3][4][5]} The roots, flowers, and leaves of Althaea officinalis are used in traditional herbal medicine to treat a variety of problems, including coughs and colds.^[6] Cough syrups that contain Althaea officinalis extracts (e.g., Phytohustil) are available in some countries.^[7][8]

Althaea officinalis is also known as “marshmallow”,^{[6][9][10][5][11][12][13]} but it should not be confused with its foam-like confectionery namesake. Dietary supplements derived from Althaea officinalis are sometimes called “marshmallow root” or “marshmallow leaf” and are often claimed to reduce inflammation, improve digestive health, and prevent coughs and colds.

Althaea officinalis extracts have antibacterial,^[14][15] antioxidant,^{[7][8][16][15][4]} and anti-inflammatory properties,^[7][8] but most of the supporting evidence for these effects is derived from cell culture (in vitro) experiments. Some of these properties have been confirmed in animal models,^{[15][17][11][18][19]} and other animal studies find that extracts from Althaea officinalis can treat wounds,^[20][18] infertility,^[15] and stomach ulcers.^[17][11] Unfortunately, these effects have yet to be explored in humans.

In some animal models of respiratory disease, extracts from Althaea officinalis also have antitussive effects (i.e., they suppress coughing).^[21][22][23] While some evidence supports this claim in humans,^{[6][24][25][26][13]} the quality of the current clinical evidence is low and some of the studies are published by product manufacturers.^[24][25] Furthermore, sometimes the specific effect of Althaea officinalis cannot be determined because extracts are combined with other plant extracts.^[13] Therefore, further high quality independent randomized controlled trials are needed to confirm the effect of Althaea officinalis on coughing, and to support its other claimed benefits.

No toxicity has been identified in animal studies^[19] and no serious side effects have been reported in clinical studies.^{[24][25][26][13]} Therefore, extracts from Althaea officinalis appear safe to consume. However, the main drawback of Althaea officinalis is that there is insufficient evidence in humans to support the numerous health claims derived from the results of cell culture (in vitro) experiments and animal studies.

Althaea officinalis extracts may suppress coughing in human trials^{[24][25][26][13]} because of their antibacterial properties, which have been shown in cell culture (in vitro) experiments.^[14][18][15] In animal studies, extracts from Althaea officinalis have also been shown to suppress the coughing reflex via a direct effect on serotonergic receptors in the nasopharynx (a part of the throat behind the nose).^[22] Extracts from Althaea officinalis can also bind to epithelial cells (a type of cell that lines the airways),^[5][9] produce a protective mucilaginous film of polysaccharides,^[5] and reduce inflammation in many cell types,^[7][16] including macrophages (a type of immune cell involved in defending against pathogens).^[8] Consequently, the cough-suppressing effects of extracts from Althaea officinalis might be the result of reduced airway inflammation. However, these possible mechanisms are speculative. Further high quality randomized controlled trials are needed to bolster the current evidence, and additional mechanistic studies are needed to fully understand how Althaea officinalis supplements might work.