Alternatively, if the biological target is not known, phenotypic drug discovery may be undertaken . This process involves the initial identification of potent compounds that give rise to the desired effect (e.g. inhibition of cell growth), with target determination performed thereafter. The lead optimisation phase in this type of drug discovery is less streamlined than that in the former method as it is conducted without guidance from target binding interactions and often relies upon the intuition of the medicinal chemist to design and synthesise compounds to explore the SAR. There are a number of obvious limitations to this approach, including the personal bias/imagination of the scientist or the availability/cost of resources. As a result, good hypotheses or key insights may be overlooked, which can lengthen the time taken to identify a lead candidate and increase costs associated with synthesising complex molecules that are later revealed to be inactive. Nevertheless, the advantage of phenotypic drug discovery, which underpins its popularity, is that hit or lead compounds are already known to be effective in their overall role (e.g., the killing of a pathogen).