BACKGROUND: From November 2014 to November 2015, an experiment in French community pharmacies replaced traditional pre-packed boxes by per-unit dispensing of pills in the exact numbers prescribed, for 14 antibiotics. METHODS: A cluster randomised control trial was carried out in 100 pharmacies. 75 pharmacies counted out the medication by units (experimental group), the other 25 providing the treatment in the existing pharmaceutical company boxes (control group). Data on patients under the two arms were compared to assess the environmental, economic and health effects of this change in drug dispensing. In particular, adherence was measured indirectly by comparing the number of pills left at the end of the prescribed treatment. RESULTS: Out of the 1185 patients included during 3 sessions of 4 consecutive weeks each, 907 patients experimented the personalized delivery and 278 were assigned to the control group, consistent with a 1/3 randomization-rate at the pharmacy level. 80% of eligible patients approved of the per-unit dispensing of their treatment. The initial packaging of the drugs did not match with the prescription in 60% of cases and per-unit dispensing reduced by 10% the number of pills supplied. 13.1% of patients declared that they threw away pills residuals instead of recycling-no differences between groups. Finally, per-unit dispensing appeared to improve adherence to antibiotic treatment (marginal effect 0.21, IC 95, 0.14-0.28). CONCLUSIONS: Supplying antibiotics per unit is not only beneficial in terms of a reduced number of pills to reimburse or for the environment (less pills wasted and non-recycled), but also has a positive and unexpected impact on adherence to treatment, and thus on both individual and public health