US Federal drug regulators have ruled that two leading anti-smoking drugs must now carry black-box suicide warnings.

The move on Pfizer's and Glaxo Smith Kline's smoking-cessation drugs, follows thousands of cases of depression and hundred of suicides in the US.

Patients of the drugs Champix and Zyban have been asked to be vigilant for suicidal thoughts and signs of depression.

2SER's Esther Han reports.