Seroxat is one of the world's biggest selling and most successful anti-depressants.
But this Panorama investigation discovers the drug may have a darker side - the programme reports that people can get hooked on it, suffering serious withdrawal symptoms when they try to come off it.
For some it can lead to self harm and even suicide. But little warning of these possible side effects accompanies the drug.
These are accusations that the drug's maker GlaxoSmithKline denies.
The programme follows one Seroxat user and charts her nine month struggle to wean herself off it.
Panorama also spoke to Dr David Healy, an expert on the drug who has had access to confidential Seroxat studies in the GlaxoSmithKline archives.