OBJECTIVES: This study investigates the extent to which geographic variation in adequacy of primary care and specialist supply explains variation in patient use of prescribed medications to treat chronic conditions. METHODS: Generalized Least Squares regression with period random effects was used on a pooled data set of monthly (May 2006 to Oct 2010) IMS Health data for 360 Metropolitan Statistical Areas (MSAs). The dependent variable was total monthly prescriptions per MSA for: (1) Statins, (2) PPIs, (3) Anti-psych, and (4) asthma/COPD. Separate regressions were estimated by therapeutic category and by payer type. Explanatory variables include monthly: (1) size of the population with the chronic condition ;(2) economic environment; (3) dummy event variables; and (4) level of Rx advertising. Estimates of the shortfall of primary care providers and specialists in each State in 2010 are included as explanatory variables. For state-level shortfall, provider demand estimates were based on national healthcare use and delivery patterns applied to each State’s population controlling for demographics, rates of uninsured, and obesity rates. RESULTS: There exists a direct correlation between estimated adequacy of primary care and specialist (cardiologist, gastroenterologist, psychiatrist, pulmonologist, and allergist) supply and volume of prescriptions. The patterns are relatively consistent across therapeutic areas. For the Statin market, each 1% shortfall of cardiologists is associated with 0.36%, 0.43%, and 0.79% decrease in Statin Rx volume for the commercially insured, Medicare, and Medicaid populations, respectively. Each 1% shortfall of primary care providers is associated with decreases in volume across in the commercially insured (0.15%) and Medicaid (0.83%) populations. CONCLUSIONS:  This research suggests that controlling for economic and population risk factors, greater inadequacy of physician supply is associated with lower use of prescriptions for treating chronic conditions. Physician shortages disproportionally affect access to medications for the Medicaid population, followed by the Medicare and commercially insured populations.