By Naomi Carr

Last updated: 02 April 2024 & medically reviewed by Morgan Blair

Codeine is an opioid analgesic medication, commonly used for pain relief. It is a widely used and abused substance and can cause several side effects, including constipation, insomnia, nausea, and drowsiness. It may also cause severe side effects, particularly if it is misused, and can lead to the development of tolerance, dependence, and addiction. [1]

Key takeaways:

Common side effects of codeine may include:

  • Constipation

  • Nausea

  • Vomiting

  • Drowsiness

  • Lightheadedness

  • Dizziness

Codeine Side Effects

What is codeine?

Codeine is an opioid medication that is similar to morphine but less potent. It is widely used and is commonly abused. Due to its abuse potential, codeine is a Schedule II controlled substance, though it is often prescribed as acetaminophen with codeine, which is Schedule III. It is typically only available in the US with a prescription, it can be purchased over the counter in other countries. [1][2]

Codeine is only available as an immediate-release tablet in 15, 30, and 60 mg strengths in the US, but in other countries, it is also available as a controlled-release capsule in 50, 100, 150, and 200 mg strengths, and as an oral concentration. It is available under several different brand names and in various combination medications, with substances such as chlorpheniramine, promethazine, and guaifenesin. [3][4]

What is codeine used for?

Codeine is prescribed for mild to moderately severe pain and can be used as a short-term, long-term, or as-needed (PRN) treatment. It is also sometimes used off-label to treat coughs, restless leg syndrome, and persistent diarrhea. [1][3]

A typical dose of codeine is 15-60mg every four hours as needed, with no more than 360mg in 24 hours. [1]

Why do people abuse codeine?

Like other opioids, codeine is highly addictive and habit-forming, although it is not as potent as morphine. Individuals might begin to abuse codeine after being prescribed the medication for pain and developing physical dependence. [1][5]

Dependence can develop after weeks of codeine use, causing the onset of withdrawal symptoms when use is reduced or stopped, and can contribute to misuse of the medication. [1]

Similarly, someone prescribed codeine might develop a tolerance, which results in reduced effects of the medication. This can also contribute to codeine abuse, as it may lead to increased use to achieve desired effects and doses that are higher than recommended or prescribed. [3]

Codeine might also be abused by individuals who have not been prescribed the medication for its analgesic or euphoric effects, as it can be obtained easily through illicit diversion or sale. Codeine might be abused by being administered in unintended ways, such as being crushed and inhaled nasally or injected intravenously. [5]One of the most common ways codeine is abused is when it is added to a concoction of cough syrup, candies, and lemonade, commonly referred to as lean.

Common side effects of codeine

It is common when starting a new medication or increasing treatment doses to experience some side effects. Often, these will reduce within a couple of weeks as the body becomes used to the substance and it is processed through the system more easily. However, if they are persistent or become worse, it is recommended to consult a doctor. Common side effects of codeine include: [1][3][4]

  • Constipation

  • Nausea

  • Vomiting

  • Drowsiness

  • Lightheadedness

  • Dizziness

  • Sweating

  • Sedation

  • Impaired concentration

  • Fatigue

  • Shortness of breath

  • Low mood

  • Euphoria

  • Anxiety

  • Insomnia

  • Blurred vision

  • Shaking

  • Weakness

  • Stomach pain and cramps

  • Reduced appetite

  • Dry mouth

  • Sexual dysfunction

  • Urinary retention

Severe side effects of codeine

In some cases, particularly if codeine is abused and taken in large doses, severe side effects can occur. These can include: [1][4]

  • Seizures, especially for those with a history of convulsive disorders

  • Cardiac issues

  • Increased risk of respiratory depression, especially for those with a history of lung or breathing issues, or when codeine is combined with another central nervous system (CNS) depressant

  • Breathing difficulties, shortness of breath, or severely slowed breathing

  • Chest pain or tightness

  • Severe change in heart rate

  • Severe weakness or dizziness

  • Hallucinations

  • Confusion

  • Rash or hives

  • Tolerance

  • Dependence

  • Addiction 

Prolonged or heavy use of codeine can increase the risk of severe side effects and is likely to result in the development of tolerance and dependence and an increased risk of addiction. [1]

When tolerance develops, the effects of the medication are reduced, which can result in the need for increased or more regular doses to achieve the desired effects. [6]

Physical dependence causes the body to become reliant on the medication and results in the onset of withdrawal symptoms if use is stopped. Common codeine withdrawal symptoms include chills, sweating, restlessness, irritability, pain, insomnia, and diarrhea. [1]

Addiction can develop with prolonged use or abuse of codeine and may occur alongside dependence and tolerance, although it is a distinct condition. Codeine addiction can result in harmful and compulsive drug-seeking and taking behaviors, impaired functioning, and reduced quality of life. [3][7]

Codeine overdose

People taking codeine may be at risk of accidental or intentional overdose with the administration of large doses. The risk of overdose is increased if codeine is combined with other CNS depressants, such as alcohol, benzodiazepines, or other opioids, and can result in respiratory depression and death. [1]

A fatal dose of codeine will vary depending on individual factors, such as how long they have been taking codeine, as well as how high their daily dose has been during treatment. A daily dose of over 360mg of immediate-release and 600 mg of controlled-release codeine has the highest risk of life-threatening effects for most individuals. [3]

Common signs of a codeine overdose include: [1][4]

  • Cold and clammy skin

  • Severe weakness and tiredness

  • Rapid, irregular, or slowed heart rate

  • Pinpoint pupils

  • Difficulty breathing

  • Stopped breathing

  • Loss of consciousness

  • Unresponsiveness 

In the event of a codeine overdose, call 911 immediately. An opioid antagonist, Naloxone, can be administered to block the effects of codeine. Other life-saving treatments may also be required. [4]

Getting treatment for codeine dependence

Often, individuals who are prescribed codeine may be gradually tapered off the medication when treatment is no longer necessary, as this can help to reduce withdrawal symptoms. A gradual taper is the standard of care for those who abuse codeine or have developed a strong physical dependence, although additional treatment may be required in these cases. [1][5]

Treatment for codeine dependence might involve inpatient care, where professionals can provide consistent monitoring and treatment of withdrawal symptoms alongside additional treatments. [5]

Medications that may be used to treat codeine dependence include: [5][6][7]

  • Opioid agonists: Buprenorphine and methadone are often used to treat opioid use disorders including codeine dependence. They can effectively reduce cravings and withdrawal symptoms, helping with detox and maintaining abstinence.

  • Clonidine: Clonidine can be used to help reduce withdrawal symptoms during tapering or opioid replacement therapies. Although it does not reduce cravings it can help manage symptoms such as increased heart rate and blood pressure, diarrhea, anxiety, and sweating.

  • Antidepressants: Antidepressants might be prescribed to help reduce withdrawal symptoms and mental health symptoms such as low mood and anxiety.

  • Benzodiazepines: Benzodiazepines might be prescribed short-term to help reduce insomnia, agitation, and anxiety. 

Therapeutic interventions, such as cognitive behavioral therapy (CBT), can also be beneficial in the treatment of codeine dependence. They can help reduce addictive behaviors, improve interpersonal relationships, manage cravings and triggers, and treat underlying mental health issues. [5][6]

Additional interventions that may be utilized throughout codeine dependence treatment include psychosocial interventions, holistic therapies, and physical health care such as pain management. [7]