Many clinically significant infectious diseases and cancer are prone to developing resistance to a single pharmacophoric therapeutic agent, and hence combining two pharmacophoric molecular entities to give a single drug, not only improves formulation properties i.e. formulating one drug is easier than formulating two or more drugs, but also can hinder the resistance mechanisms. Thus covalently linking two therapeutics in a single drug molecule as a conjugate is an appealing strategy in drug design. Drug conjugates can be dimers of identical entities i.e. homodimers. Taking as an example, bis-tacrine is a homodimer of tacrine, and its monomers are coupled to one another by means of a polymethylenic linker. On the other hand, symbiotically dimerising two different pharmacophoric entities gives a conjugate heterodimer. This is usually achieved associatively by covalently linking one pharmacophore with another, in which two different pharmacophores are readily discernible in the resulting heterodimeric conjugate; however, occasionally it is feasible to optimise a dual acting lead compound to furnish an inherently 'dual acting drug' for which different pharmacophores are indiscernible in the thus obtained heterodimer.