OBJECTIVES: In the province of Quebec, residents are either insured by the Public Prescription Drug Insurance Plan (PPDIP) or a private drug insurance. Drug cost in Quebec has three components: molecule’s price, wholesaler margin of profit and pharmacist’s fee. The first two components are regulated by the PPDIP and are the same for publicly and privately insured patients. The third component is fixed (around CAD$8.40) and regulated by the PPDIP for publicly insured patients while it is determined freely by the pharmacy owner for privately insured patients. This study aimed to compare the drug and out-of-pocket costs of Quebec residents covered by private drug insurance to those covered by the PPDIP. METHODS: We used a sample of prescriptions filled between January 1^st, 2015 and May 15, 2019 selected from reMed, a drug claims database of Quebecers. We created pairs of prescriptions that had the same DIN, quantity, days’ supply, pharmacy number but one prescription was reimbursed by a private drug insurance and the other one by the PPDIP. The differences in drug and out-of-pocket costs between private and public drug insurance were analyzed with a mixed linear model. RESULTS: Based on 78 672 prescriptions, we observed that privately insured patients had to pay CAD$6.90 (95% CI: 4.43 ; 9.36) more on average per drug prescription than publicly insured patients (CAD$43.21 vs CAD$36.31), representing a difference of 23.9%. We also found that out-of-pocket cost was on average 1.84$ (95% CI: -2.02 ; -1.66) lower per drug prescription for privately than publicly insured patients (CAD$6.61 vs CAD$8.45). CONCLUSIONS: This study showed that, on average, drug cost is substantially higher for privately insured Quebecers. Knowing that adherence is affected by drug cost, these results will be useful to help public health authorities to make informed decisions about drug insurance policies.