A SUSAR is a Suspected Unexpected Serious Adverse Reaction report, to detail adverse events encountered by test subjects participating in a clinical drug trial. They are defined by the US EPA as "Any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment."
The list of qualifying events that require filing of a SUSAR are:
SUSARs must be reported during clinical trials but are often insufficiently described in public reports describing new drugs.
Sources:
Expert Working Group (Efficacy) of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH). (August 25, 2007). "Guideline for Industry - Clinical safety data management: definitions and standards for expedited reporting." FDA Center for Drug Evaluation and Research.

