What is codeine, and how does it work?

Codeine is a sleep-inducing and analgesic drug derived from morphine. It is used to treat mild to severe pain, as a cough medicine, and for diarrhea. It is typically found in headache tablets such as Syndol, Acurate, Adco-dol, Lenapain, Lenadol, Betapyn, Propain, Pynstop, etc. Codeine belongs to a group of medicines called opioid analgesics. These are the heavyweight drugs similar to morphine and hydrocodone which are usually reserved for the treatment of the most stubborn pain. It can be used on its own or in combination with other pain killers such as paracetamol. Codeine can be used in children over 12 years of age for the short-term relief of moderate pain that is not relieved by other painkillers such as paracetamol or ibuprofen alone. Most people probably have their first encounter with codeine through the use of Syndol headache tablets.

How does codeine find and kill pain?

Codein relieves pain in two ways: first by interfering with and blocking the transmission of pain signals to the brain, and then by working in the brain to alter the sensation of pain. The precise mechanism of action of codeine is not known; however, like morphine, codeine binds to receptors in the brain (opioid receptors) that are important for transmitting the sensation of pain throughout the body and brain. Codeine increases tolerance to pain, decreasing discomfort, but the pain still is apparent to the patient. In addition to reducing pain, codeine also causes sedation drowsiness and depresses breathing.

It is important to understand that codeine neither finds nor kills pain, it simply reduces and alters the user's perception of the pain. It’s like having a sympathetic and over-enthusiastic friend who says, "Hey girl, I can help you forget your pain and everything is going to be alright. Actually, your pain is an illusion; I will help you get over it. Here, look at that cute dress in the shop window… isn’t that gorgeous?"

When your head starts pounding and you reach for Syndol tablets, it's easy to take what the medication does for granted. Once a pill or liquid solution containing codeine gets swallowed, it travels through the body and is absorbed into the bloodstream. At that point, the blood carries the medicine to different parts of the body, looking for the pain.

Note that the medicine isn't exactly going to a specific spot: codeine will go ahead and get to work, regardless of whether an area has pain or not. That's why if you have a headache you're trying to treat, you might start to feel less pain in your legs that are sore after a tough work-out.

Comparison with non-steroidal anti-inflammatory pain killers

The other class of pain killers is called non-steroidal anti-inflammatory (NSAIDs) medication. It includes aspirin, naproxen, paracetamol and ibuprofen. These are the light-weight over the counter medicines we reach for whenever we've got a headache or sore muscles. They treat aches by reducing inflammation (which can be anything from heat, fever, swelling, pain or losing movement). Say you've strained your back muscles while moving into a new apartment: the body's white blood cells go into that spot to repair the muscle, causing swelling and heat that can lead to pain. (This is one reason some pain can be good: It's your body saying, I'm hurt - go easy on me.)

Unlike narcotics, aspirin drugs are real workhorses that actually go to the source of pain and stop it. When cells are damaged, they produce large quantities of an enzyme called cyclooxygenase-2. This enzyme, in turn, produces chemicals called prostaglandins, which send pain signals to the brain. They also cause the area that has been damaged to release fluid from the blood to create a cushion so the damaged cells don't take any more of a beating. This cushion is the swelling and inflammation that goes along with our aches and pains. When we take aspirin, it dissolves in our stomachs and travels through the whole body via the bloodstream. Although it's everywhere, it only works its magic at the site of cell damage by binding to the cylooxygenase-2 enzymes and stopping them from prostaglandins. No more prostaglandins means no more pain signals. The cells at the damage site, of course, are still damaged, but we're left blissfully unaware.

Is codeine addictive?

Codeine is habit forming (addictive). Mental and physical dependence can occur but are unlikely when used for short-term pain relief. Using codeine during pregnancy can cause opioid withdrawal syndrome in the newborn, which may be life-threatening if not treated.

What are the side effects of codeine?

The most frequent side effects of codeine include:

• Lightheadedness
• Dizziness
• Nausea
• Vomiting
• Shortness of breath
• Sedation
• Allergic reactions
• Constipation
• Abdominal pain
• Rash
• Itching

Serious side effects of codeine include:

• Life-threatening respiratory depression
• Severe low blood pressure
• Adrenal insufficiency

Accidental ingestion of codeine can result in fatal overdose

Warnings and precautions

Codeine is transformed to morphine in the liver by an enzyme. Morphine is the substance that produces pain relief. Some people have a variation of this enzyme and this can affect people in different ways. In some people, morphine is not produced or produced in very small quantities, and it will not provide enough pain relief. Other people are more likely to get serious side effects because a very high amount of morphine is produced.

If you notice any of the following side effects, you must stop taking this medicine and seek immediate medical advice: slow or shallow breathing, confusion, sleepiness, small pupils, feeling or being sick, constipation, lack of appetite.

You should not take Codeine if you are sensitive to aspirin or other medicines used for the treatment of inflammation (Non Steroidal Anti-inflammatory Drugs) such as Ibuprofen.