Unknown or multiple physiological pathways

The designation "Unknown or multiple physiological pathways" is a categorical label used in pharmacology and drug discovery databases to classify therapeutic agents whose specific molecular targets have not been identified or which act through a complex, multi-faceted set of biological processes (ChEMBL, 2024). This classification is frequently applied to drugs discovered through phenotypic screening, where a desired physiological effect is observed in a whole-cell or organismal model before the underlying protein target is understood (Swinney & Anthony, 2011). It may also encompass substances like general anesthetics or certain complex natural products that modulate cellular environments or multiple signaling nodes rather than binding to a single, discrete receptor (Overington et al., 2006). Because this is not a specific biological entity, it does not possess a unique molecular structure, genetic sequence, or localized expression pattern. Instead, it serves as a placeholder to indicate that the pharmacological mechanism is either polypharmacological or currently remains a "black box" in medical science (Mullard, 2015). Consequently, drugs in this category present unique challenges for rational drug design and safety prediction, as their therapeutic and adverse profiles are often determined empirically through clinical observation rather than target-based assays.

Other names

Undetermined mechanism of actionNon-specific targetMultiple physiological targetsPhenotypic targetUnknown molecular target

The mechanism of action is either currently uncharacterized, involves non-specific physical-chemical interactions, or results from the simultaneous modulation of multiple, poorly defined signaling pathways (Swinney & Anthony, 2011).