Matthew Hill investigates the drug Champix, available on prescription in the UK to smokers who want to kick the habit. Since approving the drug in 2006, the US Food and Drug Administration has issued a safety warning about prescribing Champix to people with a history of psychiatric illness. To explore fears that the drug is linked to depression and even suicidal tendencies, Hill travels to the United States. He meets critics of Champix, asks why the clinical trials did not include people with a history of mental illness and questions the manufacturer Pfizer about the drug's safety.