Painkiller that changes form once it's inside the body

The name "codeine" comes from the Greek word kodeia, meaning "poppy head". It has been traditionally prepared from the opium poppy for many centuries and it was first isolated as a discrete chemical compound in 1832 by the French chemist and pharmacist Pierre Robiquet.

Although codeine can be extracted directly from the opium poppy, most commercially available products are made by altering the chemical structure of morphine to produce purified codeine for use as a general painkiller.

Codeine is classed as a "prodrug", meaning that it does not directly affect the body but is broken down by the liver to produce morphine, the opiod drug that is the effective painkiller. This is also highly addictive when taken repeatedly.

In 2005, the pharmaceuticals industry brought in voluntary guidelines for over-the-counter medicines containing codeine. These involved the addition of addiction warnings to packets which advised patients not to take codeine-containing pills for more than three consecutive days without talking a doctor.

Source - Independent