The mucilage of slippery elm gives it a soothing effect for coughs. Usnea also contains mucilage, which may be helpful in easing irritating coughs. There is a long tradition of using wild cherry syrups to treat coughs. Other traditional remedies to relieve coughs include bloodroot, catnip, comfrey (the above-ground parts, not the root), horehound, elecampane, mullein, lobelia, hyssop, licorice, mallow, (Malvia sylvestris),red clover, ivy leaf, pennyroyal (Hedeoma pulegioides, Mentha pulegium),onion, (Allium cepa), and plantain (Plantago lanceolata, P. major). None of these has been investigated in human trials, so their true efficacy for relieving coughs is unknown.

Lobelia contains many active alkaloids, of which lobeline is considered the most active. Very small amounts of this herb are considered helpful as an antispasmodic and antitussive agent (a substance that helps suppress or ease coughs). Anti-inflammatory properties of the herb have been demonstrated, which may be useful, since bronchitis is associated with inflammation in the bronchi.³ Lobelia should be used cautiously, as it may cause nausea and vomiting.

Eclectic physicians—doctors in turn-of-the-century North America who used herbs as their main medicine—considered lobelia to be one of the most important plant medicines.⁴ Traditionally, it was used by Eclectics to treat coughs and spasms in the lungs from all sorts of causes.⁵ A plant that originates in Africa, khella, is also considered an anti-spasmodic like lobelia. Though it is not strong enough to stop acute asthma attacks, khella has been recommended by German physicians practicing herbal medicine as possibly helpful for chronic asthma symptoms.⁶

Mullein is classified in the herbal literature as both an expectorant, to promote the discharge of mucus, and a demulcent, to soothe and protect mucous membranes. Historically, mullein has been used as a remedy for the respiratory tract, particularly in cases of irritating coughs with bronchial congestion.⁷ Other herbs commonly used as expectorants in traditional medicine include elecampane, lobelia, yerba santa (Eriodictyon californicum),wild cherry bark, gumweed (Grindelia robusta),anise(Pimpinella anisum), and eucalyptus. Animal studies have suggested that some of these herbs increase discharge of mucus.⁸ However, none have been studied for efficacy in humans.