In the UK, more than 7,600 reports of suspected adverse reactions were collected in the first two years after bupropion's approval by the Medicines and Healthcare Products Regulatory Agency as part of the Yellow Card Scheme , which monitored side effects. Approximately 540,000 people were treated with bupropion for smoking cessation during that period. The MHRA received 60 reports of " suspected [emphasis MHRA's] adverse reactions to Zyban which had a fatal outcome". The agency concluded that "in the majority of cases the individual's underlying condition may provide an alternative explanation."  This is consistent with a large, 9,300-subject safety study that showed that the mortality of smokers taking bupropion is not higher than the natural mortality of smokers of the same age.