Computerized alerts provided by health care information systems have been shown to enhance clinical practice. However, clinicians still override more than half of the alerts. This indicates that certain aspects of alerts need improvement to fulfill their purpose of supporting clinicians in decision making. This paper reports on a systematic review on studies evaluating alert specifications and their impact on clinicians' alert adherence. The review revealed that use of colors and icons to distinguish different alert severity levels and presenting high severity alerts in an interruptive fashion increases clinicians adherence to alert recommendations. Alert message contents that lack clinical importance or provide incorrect texts increase alert non-adherence. Few studies have yet focused on the impact of alert specifications on clinicians' adherence. A research agenda is needed on alert specifications and their impact on clinicians' adherence in order to develop alerts that truly support clinician decision making.