Examples

Codeine is one of the strongest cough suppressants known, along with a number of derivatives such as the dihydrocodeine-hydrocodone subgroup of opioids, and the semi-synthetics and synthetics mentioned below. Codeine is the standard by which all antitussives are measured. It suppresses coughing by direct action on the cough centre in the brain, and also decreases the rate and/or tidal volume of respiration. The below-mentioned semi-synthetics differ from codeine in such ways as lipid solubility and CNS penetration, overall side-effect profile, and duration of action.

Natural and semi-synthetic opiates with antitussive effects include codeine, ethylmorphine (also known as dionine or codethyline), dihydrocodeine, benzylmorphine, laudanum, dihydroisocodeine, nicocodeine, nicodicodeine, hydrocodone, hydromorphone, acetyldihydrocodeine, thebacon, diamorphine (heroin), acetylmorphone, noscapine and pholcodine and others.

Laudanum, also known as Deodourised Tincture of Opium and Denarcotised Opium Tincture due to the removal of narcotine, an opium alkaloid which causes nausea, is a whole-opium preparation which has both morphine and codeine in it in addition to other alkaloids which relax smooth and striated muscles. It is of value in cases where the disease is causing other problems for the patient which could benefit from the actions of morphine. Laudanum is still manufactured and used throughout the world at present although it is more common to use paregoric (several times more dilute than laudanum), solid forms of opium, or alkaloid mixtures such as pantopon. Morphine by itself has marginal antitussive properties.

Noscapine and pholcodeine are natural opium alkaloids which have some antitussive effect and tend not to have a full spectrum of narcotic effects and low or non-existent physical dependence or addiction liability; preparations thereof are often available over the counter in many countries. Noscapine is used less often these days and has been removed from the standard recipe for pantopon, omnopon and similar opium alkaloids salts preparations in many pharmacopeias because of concerns about carcinogenicity a number of years ago and clinical experience that noscapine is not a necessary or effective component of pantopon-type drugs.

Ethylmorphine is almost identical to codeine in effects and chemistry and is in structure the closest relative of codeine (codeine is also known as methylmorphine). Both ethylmorphine and codeine are partially changed to morphine in the liver.

Benzylmorphine (Peronine), is also closely related to codeine and the strong opioid analgesic myrophine.

Dihydrocodeine, a close chemical relative of codeine which is usually the number-two prescription narcotic antitussive in countries in which hydrocodone is not available, is related to the strong opioid dihydromorphine in the same way codeine is to morphine and a percentage of it is changed to dihydromorphine in the liver. Dihydrocodeine is base of a number of other semi-synthetic opioids, many of which are also effective antitussives.