What Is Codeine?

Codeine, like many other drugs, can interact with others, enhancing its effects. Left unchecked, it can lead to serious toxic conditions.
What Is Codeine?

Written by Equipo Editorial

Last update: 16 December, 2022

Codeine is an active principle, derived from opiate compounds, that acts centrally. It’s a powerful pain reliever that’s used for the relief of moderate pain. In addition, it also has antitussive properties.

Some trade names of this active principle are Codeisan, Tosein, Notusin, and Fludan. Codeine can be taken together with other pain relievers such as dipyrone or paracetamol in order to enhance its effect. Of course, this should always be under medical supervision; you should never self-medicate.

This analgesic and antitussive medication comes in different pharmaceutical forms such as syrup, tablets, or injectable ampoules. It’s sold in pharmacies under medical prescription.

Due to its effects, codeine is recommended for the treatment of :

  • Pain: As we have said, it’s used to treat pain of moderate intensity, and pain that isn’t relieved by other analgesics.
  • Dry cough: Codeine blocks the cough reflex centrally.

Next, we will see the following characteristics of this drug:

  • Mechanism of action: How does the drug exert its effect in the body?
  • Pharmacokinetics: What happens to codeine in the body?
  • Adverse reactions.
  • Interactions.
A woman taking codeine.

Mechanism of action

In addition to its analgesic effect, codeine is effective in reducing coughs, reducing the maximum intrathoracic pressure, and even suppressing the cough completely.

These effects come from its ability to:

  • Depress the bulbar center of the cough
  • Induce a local anesthesia
  • Decrease secretions
  • Reduce bronchoconstriction
  • Promote the expulsion of secretions

So, how does it achieve all this? Codeine is a weak agonist that works at the μ-opioid receptors of the bulbar centers. As for the analgesic effects, these are due to the conversion of this active principle into another: morphine.

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Pharmacokinetics of codeine

Pharmacokinetics encompasses the absorption, distribution, metabolism, and elimination processes of drugs.


Despite existing in different pharmaceutical forms and formats, the most used presentation is in tablets for oral administration. For this reason, we’ll focus on this path. In this sense, it’s well absorbed orally and its effects begin to appear 30-60 minutes after administration.

The maximum effects are observed after 60-90 minutes and are maintained for about 5 hours. The maximum antitussive activity is reached one or two hours after its administration and also lasts approximately 5 hours.


Regarding its distribution, it binds in a low percentage to plasma proteins – around 7% – and so it won’t interact much with other drugs that bind in a higher proportion.

It’s important to note that codeine crosses the placental barrier. Because of this, it can’t be administered to pregnant or lactating women .


Codeine undergoes liver metabolism. Metabolism is a set of biochemical reactions that the drug undergoes in the body in order to make it more soluble and thus promote its elimination.

The main metabolite is morphine, which is responsible for carrying out effective analgesic action. Local central nervous system conversion of codeine to morphine via liver enzyme systems may explain the analgesic effect of codeine despite low plasma levels of morphine.


The elimination half-life ranges from 3-4 hours for codeine to 2 hours for morphine. This parameter indicates the time required to remove half the blood concentration of the drug.

Finally, both the metabolites and the unchanged codeine are eliminated via the kidneys. However, a negligible part can also be eliminated in the feces.

A woman on the toilet.

Adverse reactions

Codeine can cause respiratory depression. Therefore, emphysematous patients must be careful as this drug can aggravate this condition.

On the other hand, older people have to be careful with codeine in the following cases:

However, this drug has a series of advantages compared to other opioids, which is that it doesn’t produce dependence, doesn’t produce deep depression and doesn’t induce comas.

Other side effects that you may have are:

  • Dizziness
  • Drowsiness
  • Constipation
  • Rashes
  • Nausea and vomiting
  • Others


Codeine, like many other drugs, can interact with others, enhancing its effects. Left unchecked however, it can lead to serious toxic conditions. Therefore, if you’re going to start a treatment with this drug, you must tell your doctor if you’re taking any other substance.

Some of the most common drugs and substances it interacts with, and which enhance its sedative action are:

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