Co-codamol is a painkiller that combines two active ingredients: codeine and paracetamol. It comes in tablet or capsule form and is used for short-term relief of moderate pain that doesn’t respond well to paracetamol alone. The lowest strength (8/500) is available over the counter in the UK in packs of up to 32 tablets, while the stronger versions require a prescription.
What’s Inside Co-Codamol
Every co-codamol tablet contains 500mg of paracetamol. What varies is the amount of codeine. The three standard strengths are 8/500, 15/500, and 30/500, where the first number is the milligrams of codeine and the second is the paracetamol. So an 8/500 tablet has 8mg of codeine, while a 30/500 tablet has nearly four times as much.
Only the 8/500 strength is sold without a prescription. The 15/500 and 30/500 strengths are prescription-only because higher doses of codeine carry greater risks of side effects and dependence.
How It Relieves Pain
The two ingredients work through different pathways, which is why combining them can be more effective than either one alone. Paracetamol works mainly in the brain, where it reduces the production of chemical messengers involved in pain signaling. It also lowers fever, though it doesn’t reduce inflammation the way ibuprofen does.
Codeine is an opioid, but it doesn’t do much on its own. Your liver converts a small portion of each dose into morphine, and that morphine is what actually dulls the pain. Codeine has roughly one-sixth the pain-relieving strength of morphine. Together, the two ingredients cover overlapping but distinct pain pathways, which is why the combination often works when paracetamol by itself falls short.
How Quickly It Works
You can expect co-codamol to start working within 30 to 45 minutes of taking it. The pain relief peaks at about one to two hours and generally lasts around four hours. That timing is why the standard dosing schedule spaces tablets roughly four to six hours apart.
Common Side Effects
The codeine component is responsible for most of co-codamol’s side effects. Constipation is one of the most predictable. Codeine slows the movement of your digestive tract, and this effect doesn’t fade much with continued use. If you’re taking co-codamol for more than a day or two, you may need to increase your fiber and fluid intake or use a mild laxative.
Other common side effects include drowsiness, nausea, dizziness (especially when standing up quickly), and itching. Some people also experience lightheadedness or a general sense of sedation that makes it harder to concentrate. These effects tend to be more pronounced at the higher prescription strengths.
The most serious risk with any codeine-containing medicine is respiratory depression, where breathing becomes dangerously slow and shallow. This is rare at normal doses in healthy adults, but the risk rises significantly if you combine co-codamol with alcohol, sleeping pills, or other sedating medications.
Why Alcohol Is a Serious Risk
Drinking alcohol while taking co-codamol amplifies both the sedation and the breathing suppression. Alcohol and codeine both depress the central nervous system, and together they can slow breathing to a dangerous degree. This risk is highest during the first 24 to 72 hours of treatment or whenever your dose increases, but it applies any time you mix the two.
Genetics and How You Respond
Not everyone converts codeine to morphine at the same rate. A liver enzyme determines how much morphine your body actually produces from each dose, and the gene controlling that enzyme varies widely across the population.
Some people are “ultra-rapid metabolizers,” meaning they convert codeine to morphine faster and more completely than average. For these individuals, a standard dose can produce unexpectedly high morphine levels, raising the risk of serious side effects including dangerous breathing suppression. This variation has caused fatal reactions in rare cases, including the death of a breastfed newborn whose mother was taking standard codeine doses.
On the other end of the spectrum, “poor metabolizers” produce very little morphine from codeine, so the drug provides almost no pain relief for them. If you’ve taken codeine-based painkillers in the past and felt no benefit, this genetic difference may be why. Clinical guidelines recommend that both ultra-rapid and poor metabolizers avoid codeine entirely and use alternative painkillers instead.
The Paracetamol Safety Limit
Because each co-codamol tablet contains 500mg of paracetamol, taking two tablets gives you a full 1,000mg dose, which is the same as two standard paracetamol tablets. This is important to keep track of because paracetamol overdose is one of the most common causes of acute liver failure. If you’re taking co-codamol, you should not take additional paracetamol on top of it. The same goes for any other combination product that contains paracetamol, such as cold and flu remedies. It’s easy to accidentally double up without realizing it.
Dependence and Short-Term Use
Codeine can cause physical dependence in as little as three days of regular use. Your body adjusts to the presence of the opioid, and stopping abruptly can trigger withdrawal symptoms like restlessness, sweating, muscle aches, and irritability. Over-the-counter co-codamol packs in the UK are limited to 32 tablets specifically to discourage prolonged use.
Co-codamol is designed as a short-term option. For ongoing pain, other approaches are typically more appropriate and carry fewer risks. If you find yourself reaching for co-codamol regularly, that’s a signal the underlying pain needs a different management strategy rather than repeated doses of an opioid combination.