BACKGROUND: Public prescription drug plans vary markedly across Canada. To address perceived inequities in coverage across provinces, the February 2003 First Ministers' Accord on Health Care Renewal committed to ensuring that all Canadians have reasonable access to catastrophic drug coverage. A national standard for "reasonable" catastrophic coverage has yet to be formally defined. OBJECTIVE: To compare the private financial burdens from prescription drugs that Canadian households would face if each of the current provincial pharmacare models were adopted as the national standard. METHODS: Through simulation modelling, we computed household private financial burden by applying the cost-sharing rules from provincial drug plans to a nationally representative set of 4,860 household types differing in size, age composition, income and drug expense levels. The proportions of households that would face private out-of-pocket payments exceeding critical, or catastrophic, percentages of household income were calculated. RESULTS: Private financial burden due to prescription drug costs varies considerably across provincial pharmacare models. Comprehensive, tax-financed pharmacare models that limit out-of-pocket expenditures to a given percentage of income, such as those found in British Columbia, Saskatchewan, Manitoba and Ontario, provide the greatest protection against catastrophic prescription drug costs. There appears, however, to be no "gold standard" for an acceptable financial burden to be borne by patients.