Recent studies have linked patient misunderstanding of label instructions for as needed (PRN) medications to dosing errors. This study conducted a preliminary field test of patient-centered PRN label instructions. Patients participated in a hypothetical dosing experiment and were randomized to a patient-centered label (referred to as "Take-Wait-Stop") or standard label. Participants were asked to demonstrate dosing the medicine over 24 hours. Three types of independent dosing errors were measured: (a) taking more than two pills at one time, (b) exceeding the maximum daily dose, and (c) waiting fewer than 4 hours between doses. Generalized linear models were used to assess the association between label type, health literacy, and sociodemographic characteristics. Participants' mean age was 39.8 years, 62.1% were female, 43.7% were White, and 72.4% had adequate literacy. Of participants, 31.8% who were shown the standard label demonstrated taking in excess of 6 pills in 24 hours compared with only 14.0% of participants who were shown the Take-Wait-Stop label (p = .05). Overall, only 1 person demonstrated he would take more than 2 pills in a single dose. Of the standard label group, 20.5% demonstrated dosing intervals of fewer than 4 hours compared with 23.3% of the Take-Wait-Stop label group (p=.75). In a multivariate model, participants who were exposed to the standard label were 2.5 times more likely to exceed the recommended maximum daily dose (95% CI [1.05, 7.70], p=.03). The Take-Wait-Stop label was beneficial in preventing participants from exceeding the maximum dose in 24 hours, although it did not significantly reduce other dosing errors.