The cough reflex is intended to expel mucus and other unwanted material from the breathing passages. However, sometimes it takes on a life of its own and causes an unproductive cough that seems to serve no purpose except to keep you awake.

The most common cause of coughing is a viral infection. Sometimes a chronic cough may indicate asthma, either allergic or created temporarily by a respiratory infection. Other causes of cough include sinus drainage tickling the throat and chronic bronchitis.

First and foremost, medical treatment for cough involves treating the underlying condition, if possible. When appropriate, cough suppressants may be prescribed as well, to hold coughing to manageable levels. Most cough remedies contain codeine or the codeine-like drug dextromethorphan to suppress the cough reflex, as well as guaifenesin, which is thought to loosen mucus. Other common ingredients such as decongestants and antihistamines do not directly affect coughs. Unfortunately, there is no reliable evidence that any over-the-counter cough suppressant actually works.¹ Furthermore, while it is often said that prescription codeine cough syrups are more effective than dextromethorphan, one study found that neither codeine nor dextromethorphan reduced night-time coughing in children to any greater extent than placebo.² In another study, prescription codeine cough syrup failed to prove more effective than dextromethorphan.³

Proposed Natural Treatments

Although many herbs have been used historically to treat coughs, none has been shown effective in a double-blind, placebo-controlled trial. Without such trials it is impossible to know whether a treatment really works, regardless of its reputation. (For a discussion of the many ways in which people can be fooled into thinking that an ineffective treatment is effective, see Why Does This Database Rely on Double-blind Studies?) A few studies that lack a placebo group are sometimes cited in support of traditional cough remedies, but these are almost as unreliable as completely unscientific anecdotes.

Weak evidence indicates that the herb marshmallow may help soothe coughs.⁴ The herb coltsfoot has been used since ancient times to relieve cough; its scientific name, Tusillago farfara, means “cough dispeller” in Latin. However, there is no scientific evidence to indicate that coltsfoot actually works. Furthermore, the root of the plant contains high levels of liver-toxic pyrrolizidine alkaloids. The leaves and flowers are safer, but they also may contain these toxins.

Many herbs are categorized as mucilaginous (gluey), and are said to coat the throat. These include marshmallow, mullein, plantain, and slippery elm. The herbs ivy leaf, primula root, and soap bark contain chemicals called saponins, which are said to loosen mucus. Other herbs used for coughs include elecampane, garlic, horehound, hyssop, lobelia, and licorice. Essential oils such as anise, eucalyptus, fennel, peppermint, and thyme are often included in cough preparations or added to a vaporizer. As noted above, there is no meaningful scientific evidence that any of these treatments are effective. However, since much the same situation exists for standard cough suppressants, they may be worth trying.

Chocolate contains the stimulant substance theobromine. One study hints that theobromine might have a cough-suppressant effect.⁶

One study found that a sesame oil cough preparation was no more effective than placebo.⁵

The most common cause of a cough is a respiratory infection; for this reason, herbs and supplements used to treat colds may be worth considering as well.