Oral anticancer drugs have the advantages of convenient and flexible administration, however, they also face some new problems related to their oral preparation. Herein we describe a case of advanced non-small-cell lung cancer patient treated with gefitinib who had long-term adverse reactions of rashes and diarrhea, and his rashes disappeared after taking alkaline soda, and then reappeared after stopping drinking it. Imaging progress was also observed. To our knowledge, this is the first report on the effect of alkaline food on gefitinib-induced rashes dynamic change. In this case, the rash acted as a signal of therapeutic efficacy. Clinicians and pharmacists should be aware of potential and common factors that affect drug efficacy and strive to achieve the best therapeutic results.