OBJECTIVES: To evaluate effect of side effect characteristics (frequency and severity) and stylistic factors (plain language or plain language combined with numeric frequency) on risk perception of side effects. METHODS: About 100 participants were randomly presented with four of eight conditions with information about medication side effects in a 2 (side effect frequency: low, high) X 2 (side effect severity: mild, severe) X 2 (communication style: plain language, plain language combined with numeric frequency) experimental design. The participants were then asked to rate their risk perception with each of the four conditions. Test for analysis of variance was performed. RESULTS: As compared to plain language only, the use of combination of plain language and numeric frequencies to communicate side effect information lead to an increase in risk perception for mild side effects of high frequency (difference between mean risk perception scores = 25.30, p<0.001). The mean risk perception scores did not differ significantly across the two communication styles for severe side effects of high frequency, severe side effects of low frequency and  mild side effects of low frequency. With plain language communication style the difference between mean risk perception scores across two frequency levels was 42.68 (p<0.001) for mild side effects whereas that for severe side effects was 61.59 (p<0.001). Similar effects were seen with combination communication style (mild side effects: difference between means= 70.34, p<0.001; severe side effects: difference between means= 70.07, p<0.001). With communication style and frequency kept constant, change in severity did not have any effect on the risk perception scores. CONCLUSIONS: Frequency of side effects play a major role in evaluation of personal risk of side effects. Stylistic factors also affect risk perceptions to some extent based on the effects of frequency. These results may help healthcare providers in utilization of appropriate methods for communicating risk of medication side effects.