Side effects for prescription drugs vary in their severity and frequency of occurrence. Understanding the status of a given drug on both these dimensions is important for physicians during the prescribing process, for regulators and industry in the approval and safety review process, and for patients in the compliance process. There is a wide variety of terms used to describe severity and frequency information in both professional information sources (such as the approved label) and patient sources (such as pharmacy leaflets). The experiments reported here examine how people understand these terms, whether laypersons interpret them in the same ways as professionals, and the consequences of providing terms in alternative linguistic, numeric, and visual forms. This work holds implications for risk communication for healthcare providers and patients, the needs of low-literacy and low-numeracy audiences, and health literacy in general.