2nd plot.
From the 20917 events data, the direct link from a single ZYRTEC to a particular adverse reaction is not possible to build. However, with statistics, the drugs taken at the same period with ZYRTEC, could be playing a drug-drug interaction in a synergistic way, which leads to adverse reaction. In this network,  all drugs shown here relate to some adverse events. Clearly, there are GROUPs of drugs, which means they were taken together and highly likely contributing to some events. Zyrtec is one of the mostly connected hub (shown by size of oval). We could benefit from the co-occuring drug-drug pairing statistics,  to avoid severe adverse reactions.

1st plot: The openFDA deposits adverse reaction events. The event data from the reporters who got adverse reaction at the same time of taking ZYRTEC, a popular anti-histamine OTC, were retrieved. The patient info, such as onset age, weight, sex, other drugs taking, and adverse reactions, were cleaned up and analyzed. This plot shows that, comparing male and female reporters, a portion of young males (less than 25 yrs old) are distinctly subject to some adverse reactions.