In this paper we use three disparate examples to highlight the relevance of historical methods in the context of ethnobotany and ethnopharmacology. Unfortunately, in ethnopharmacology we have only very few examples where such historical depth is possible. On the other hand the first hand data available through ethnopharmacological research, may be of relevance for interpreting historical information. Three distinct methods were used successfully in the retrospective exploration of diachronic data. In order to gain an insight into historical developments in the use of plant species and evolution of pharmacopoeias we used a botanico-historical approach (Rosmarinus officinalis), one that combines linguistic and statistical methods (Popoluca/Mixe), and one that uses historical documentary evidence (Ch'orti). We hope that this methodological discussion encourages a wider use of such historical methods in ethnopharmacology and related areas of research.