There are a number of different reasons why paracetamol and codeine are combined to create co-codamol/Zapain. Here are a few of the main reasons as to why this is done: Paracetamol and codeine combinations provide greater pain relief than that achieved with paracetamol alone. Single-dose studies show a slightly increased analgesic effect (pain relief) when codeine is added to paracetamol A paracetamol/codeine mixture is recommended when more pain relief is needed In short, the combination of codeine and paracetamol offers better pain relief than paracetamol or codeine when they are taken alone. It is also a better option than using larger doses of either medication alone. Large doses of paracetamol can be hard on the liver. Large doses of codeine is more likely to cause side effects. As well as this, addiction is another concern when someone uses larger doses of codeine.