Medicines containing opiates can include cough/cold treatments, painkillers, analgesic tablets and capsules, and some diarrhoea medication, according to the Over-Count Drugs Information and Advice Agency.

A type of opiate, codeine has the same roots as heroin and cocaine; in fact, in 1898 a German company patented heroin and began to sell it as a cure for the common cough.

Codeine acts as a depressant on the central nervous system, and effects can include euphoria and relaxation but also mental detachment.

During a recent interview with the BBC, a neurologist was quoted as saying that it "took as few as six or eight [painkiller] tablets a week", consumed over an extended period, to develop dependency.

Some of the risk in over-the-counter (OTC) preparations is also linked to paracetamol content. While the drug is convenient due to its rapid absorption properties, even in limited doses it can damage the liver. Overdoses can be fatal. Paracetamol was introduced in the UK in 1956 as a prescription-only drug; it was then added to opioid analgesics such as codeine and dihydrocodeine after 1963.

White-collar employees working long hours and prone to tension headaches are those most likely to become addicted to painkillers, according to Dr Alan Wear, medical director of the rehab centre Priory Hospital Marchwood in Southampton. What starts as "a couple of paracetamol before work" can soon escalate into "frightening quantities" of tablets on a daily basis, he says.

Others vulnerable to addiction include those taking treatments for pre-menstrual pain, back pain, or insomnia.

Dr Robert Lefever, director of Promis rehabilitation clinics, notes that painkillers can become "just as addictive" as illegal drugs. The difficulty, however, lies in recognising an addiction to a drug that does not initially appear 'serious'. ; ;