Concerns have been expressed that large numbers of nonvalue-added reports have been accumulating in adverse drug reaction (ADR) databases, for example, via patient support programs. We performed an assessment of the impact of such reports, which we refer to as "precautionary reports," on safety signal detection in the Netherlands. The case narratives of ADR reports of three case products were screened with text-mining algorithms to identify those reports that lack a causal relationship with the suspected medicinal product. We demonstrate that precautionary reports impede the optimal use of the pharmacovigilance system by, on the one hand, masking safety signals and, on the other hand, creating spurious signals. The precautionary reporting bias and its suppressing effect on statistical signal detection results in an altered adverse event safety profile. The findings from this study highlight the need for a better alignment between regulatory authorities and marketing authorization holders regarding pharmacovigilance guidelines.