‌It targets the opioid receptors in the brain and other organs to produce effects similar to morphine, providing significant pain relief. The NHS often prescribes codeine for post-operative pain or injury-related pain, especially when other painkillers like paracetamol and ibuprofen are ineffective. ‌View 3 Images Codeine is regularly prescribed for pain relief (Image: Getty Images)Common side effects associated with codeineDespite its effectiveness as a pain reliever, codeine can have several side effects, particularly when used for extended periods. How long you should take codeineThe length of time you'll need to take codeine varies considerably depending on how long pain relief is required. In certain instances, you might only need codeine for several days, making you less prone to developing any symptoms.