A method is provided for increasing the permeability of skin or mucosal tissue to transdermally administered nonsteroidal anti-inflammatory drugs (NSAIDs). The method involves use of a specified amount of a hydroxide-releasing agent, the amount optimized to increase the flux of the NSAID through a body surface while minimizing the likelihood of skin damage, irritation or sensitization. Formulations and drug delivery systems for co-administering a hydroxide-releasing agent with an NSAID are provided as well.