In case of single label prediction, we predict single best isoform responsible for metabolizing a drug/substrate. In other words In case of single isoform prediction, we are predicting isoform which have highest probability of metabolizing a compound. It does not mean that this compound is non-substrate for other isoform
It has been shown in previous studies that a drug can be metabolized by more than one CYP isoform. This option allows users to predict multiple labels/isoforms for a substrate.