The clinicians depend upon the FDA labeling of new drugs. The side effects listed in the labeling are derived from data submitted by the drug company making the drug. The side effects in clinical practice are far more frequent and serious then the ones reported in the FDA labels.
The latest fad drug for anticoagulation is Dabigatran, sold as Pradaxa. The FDA labeling says it is as effective as Coumadin, maybe more. The side effects of bleeding are comparable with the only drawback that there is no effective antidote for dabigatran.
Within a few months of its introduction dabigatran was responsible 505 instances of serious side effects including 65 deaths. Coumadin was noted to cause 176 instances. These figures are for first quarter of 2011. Since the total number of patients on Coumadin and on dabigatran was not given, it is not a comparable statistic. But it is very likely that the number of patients on Coumadin far exceeds the number on dabigatran.
Annals of Medicine, 3 July 2012 157:1, 66.