We examine the release of two highly hydrophilic drugs, nicotine and caffeine, from poly(epsilon-caprolactone) (PCL) matrices. We find that the dominant mechanism for drug release is drug diffusion through the PCL matrices. As a result, the rate of drug release (defined by the amount of drug released per unit time) decreases exponentially with time. Coating the drug-carrying particles with a drug-free PCL layer significantly changes the release profile: instead of exponential decay, the release rate exhibits a peak whose location (time) and magnitude vary with the diffusion coefficient of the drug in the polymer and the thickness of the coating. As a result, coating may be used to control the release rate and obtain a relatively constant rate over a period of time. (c) 2007 Wiley. Periodicals, Inc.