Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) result from genetic
defects of heme biosynthesis that cause life-long, painful cutaneous sensitivity to light.
The objective of this study is to determine the efficacy and safety of oral cimetidine
administration for treatment of the protoporphyrias. Efficacy will be based on protoporphyrin
levels, photosensitivity, and quality of life questionnaires.