What are the dangers of Codeine?

What is Codeine?

Codeine is a commonly prescribed painkiller used to treat mild to moderate pains or when traditional painkillers don’t seem to work. Weaker strengths of Codeine can be bought over-the-counter, though higher strengths of Codeine are available on prescription.

Codeine is an opiate which, when metabolised by the liver, turns into morphine. It is used to treat all manner of pains, as well as several other maladies such as coughs, diarrhoea and irritable bowels.

As a painkiller, Codeine can be effectively combined with other drug treatments to produce greater results. For example, Codeine can be used to suppress pain from an injury whilst ibuprofen treats the inflammation. However, a doctor should always be consulted to determine if this treatment is right for you.

Over 361,000 kilograms of Codeine are produced per year, making it the most common opiate in the world. It has had a shifting legality since it was first isolated by Pierre-Jean Robiquet in 1832. In the UK, Codeine is a Schedule 5 Controlled Substance, meaning that it is on the lowest tier of controlled substances due to its low strength.

How does it work?

Codeine acts as a prodrug (a drug which transforms inside the body) that is metabolised (converted by the liver) into morphine when combined with an enzyme (P450) in the body. The Codeine then affects opioid receptors in the brain, latching onto them and mimicking endorphins - the body’s natural painkiller.

If the enzyme needed to metabolise Codeine into morphine is suppressed or inhibited, the pain relieving effects can be muted, rendering the drug ineffective.

The pills must be dissolved in the stomach and metabolised by the liver before they begin to reduce pain symptoms. This usually takes less than an hour and can provide pain relief for up to 6 hours after administering.

Codeine is sometimes combined with other painkillers, such as Paracetamol (Co-codamol) or Ibuprofen (Nurofen Plus). These combinations are more effective against pain than either drugs on their own. Additionally, the combination of codeine and Ibuprofen offers the additional benefit of reducing inflammation. Nurofen Plus and lower strength Co-codamol can be bought over-the-counter from pharmacies.

When taking combined analgesics, you must be careful with other medicine use. If you are taking a combined codeine and paracetamol painkiller, you should not take any other medicine which contains either codeine or paracetamol. Likewise, if you are taking a combined codeine and ibuprofen painkiller, you should not take any other medicine which contains either codeine or ibuprofen. 

Taking combined analgesics with other painkillers (e.g. taking paracetamol with Co-codamol) can increase your risk of accidental overdose. For further advice on taking combined analgesics with other medicines, speak to your doctor or a pharmacist.

Side Effects

As with most medicines, Codeine can cause a number of side effects, though not everyone experiences these.

Side effects are usually reduced over time as the body becomes adjusted to the drug, however a doctor should be consulted if any side effect becomes particularly severe.

The common side effects of Codeine are:

  • Nausea
  • Vomiting
  • Constipation
  • Dizziness
  • Sleepiness or fatigue
  • Dry mouth
  • Sweating
  • Stomach pains

Is Codeine safe for me?

As a prescription drug, it is ultimately up to your doctor to decide if Codeine is safe for you. However, there are several things that can exclude someone from using Codeine for their own safety:

  • Pregnancy or breastfeeding
  • Liver or kidney problems
  • Enlarged prostate
  • Issues passing urine
  • Breathing problems (such as Asthma)
  • Low blood pressure
  • An abnormal heart rate
  • Thyroid or adrenal gland problems
  • Epilepsy
  • Gallstones
  • Constipation or other bowel problems
  • A recent head injury
  • Dependency on drugs or alcohol

Codeine can inflict an adverse effect cognitive functions. Because of this, it is strongly advised to speak to your doctor about your prescribed codeine to determine whether you are eligible to drive. If it is suspected that your driving is being affected by prescription medication, you could be subject to a “field impairment assessment” or a roadside drug test. Therefore, it is imperative that you speak to your doctor to determine whether you will be fit to drive while taking medicine containing Codeine.

Side effects and interactions can impact people in different ways, so it is important to understand how your body reacts to Codeine. If you are on another drug treatment, even something as commonplace as paracetamol, make sure to inform your doctor before being prescribed Codeine. Certain drugs, such as alcohol, HIV/AIDS medications, antihistamines, and illicit substances, can interact with Codeine which may prevent the medicine from working, exacerbate side effects or even cause overdose, coma and death.

If you are unsure on whether another treatment you are taking could pose a risk of interaction with Codeine based painkillers, speak to your doctor. Always read the patient information leaflet that comes with your treatment which provides a list of ingredients, specific instructions on how to take your medicine, and any cautions, interactions and exemptions which will need to be taken into consideration before taking your medication.

It is not safe for women who are pregnant or breastfeeding to take Codeine. Opioids in pregnant women can cause neonatal abstinence syndrome - a condition where the baby suffers withdrawal symptoms of the drug you’ve taken while pregnant. Opiates can also pass onto a newborn baby through breast milk. If you are concerned about the risks that opiates pose to your unborn baby, speak to your obstetrician.


Codeine taps into the brain’s reward system, causing the brain to fire neurons containing dopamine. Dopamine is a highly addictive chemical that is fired during pleasant experiences such as sex, exercise or achieving a goal.

Over time, your brain will become accustomed to producing more dopamine than it normally would which means that, in order to get the same boost of neurotransmitters caused by the Codeine, you would need to seek more of the stimuli which triggered it in the first place. This is what leads to addiction and tolerance.

Most people who take prescription painkillers do not become addicted to them.

To reduce the risk of addiction from occurring, doctors may taper the dosage of Codeine. Tapering of medications allows the user to slowly wean themselves off the drug by taking smaller quantities over time. Codeine should not be used for a prolonged period due to the risk of addiction and dependence.

Codeine addiction can be subtle, but it can be recognised by these signs:

  • Drowsiness
  • Mood swings
  • Anxiety
  • Depression
  • Decreased appetite
  • Itching
  • Constipation
  • Stomach pain
  • Slow breathing
  • Visual disturbances

As Codeine painkillers are taken when needed, it’s easy to accidentally take more Codeine than is required. Taking too much Codeine poses a significant risk to your health. If you accidentally take too much Codeine, seek immediate emergency treatment and ensure you have the product packaging with you to inform doctors of exactly what you have taken. You may have taken too much Codeine if you experience any of the following symptoms:

  • Cold, wet skin
  • Light-headedness
  • Slow and heavy breathing
  • Muscle twitches
  • Blue lips or fingernails
  • Spasms in the stomach and intestines

Codeine overdose is extremely unlikely if you are following doctors orders. An overdose of Codeine is typically an indication of addiction or abuse. If you are following the guidance given by a healthcare professional, you can mitigate the risk of addiction considerably.

If you believe that you are becoming addicted to Codeine, speak to your GP or prescriber for advice.

For help with addiction, we encourage you to speak to your GP. You can also visit Talk To Frank to find your nearest support centre.

The NHS has a list of services which offer advice about drug use and abuse here.

Codeine can be an effective form of pain relief when used under the instruction of a healthcare professional. If you have any questions about whether Codeine based pain relief is right for you, speak to your GP or a pharmacist.