The main objective of this study is to gain an exploratory sense of the relationships between the phenotypes (response to drugs) employing the genome‐wide association studies (GWAS) summary statistics for searching underlying contribution of pleiotropy across the associated SNPs to this relationship. The findings in this study show that the effect size should be weighted appropriately, depending on the nature of assumption made for conducting phenotype clustering based on GWAS summary. Thus the methods used were helpful for exploring workable clusters of related drugs on the basis of the effect size of the shared associated SNPs when weighted with SNP-sharing strength. The presence of strong correlation between the weighted fixed effect size and the principal components provides a possibility of using principal component regression for predicting the effect size of association of a drug response with SNPs. Overall, the phenotypic pattern of drugs and associated SNPs revealed by this study are expected to help in future for understanding aetiological basis of different drugs by highlighting relevant biological pathways.