Medical devices implanted or otherwise used in a mammal are made less prone totrigger adverse reactions by use of gas cluster ion-beam (GCIB) surfacemodification adhere various drug molecules directly into or onto the surfaceof medical devices, and optionally building adhered drug layers upon the firstadhered layer to obtain a desired drug elution profile. This is accomplishedwithout the need for a polymer or any other binding agent to retain the drug.