Artificial
intelligence (AI), and, in particular, deep learning
as a subcategory of AI, provides opportunities for the discovery and
development of innovative drugs. Various machine learning approaches
have recently (re)emerged, some of which may be considered instances
of domain-specific AI which have been successfully employed for drug
discovery and design. This review provides a comprehensive portrayal
of these machine learning techniques and of their applications in
medicinal chemistry. After introducing the basic principles, alongside
some application notes, of the various machine learning algorithms,
the current state-of-the art of AI-assisted pharmaceutical discovery
is discussed, including applications in structure- and ligand-based
virtual screening, de novo drug design, physicochemical and pharmacokinetic
property prediction, drug repurposing, and related aspects. Finally,
several challenges and limitations of the current methods are summarized,
with a view to potential future directions for AI-assisted drug discovery
and design.