Organometallic compounds containing mercury (e.g., thiomersal) and arsenic (e.g. Salvarsan) had a long history of use in medicine as nonselective antimicrobials before the advent of modern antibiotics.   
Titanocene dichloride displays anti-cancer activity, and [[dichloridobis((p-methoxybenzyl)cyclopentadienyl)titanium|dichloridobis[(p-methoxybenzyl)cyclopentadienyl]titanium]] is a current anticancer drug candidate.  Arene- and cyclopentadienyl complexes are kinetically inert platforms for the design of new radiopharmaceuticals.
Furthermore, there have been made studies utilizing exogenous semi-synthetic ligands; specifically to the dopamine transporter, observing increased resultant efficacy in regard to reward facilitating behavior (incentive salience) and habituation, namely with the phenyltropane compound [[List of phenyltropanes#η6-3β-(transition metal complexed phenyl)tropanes|[η-(2β-carbomethoxy-3β-phenyl)tropane]tricarbonylchromium]].
Carbon monoxide releasing organometallic compounds are also actively investigated, due to the importance of carbon monoxide as a gasotransmitter.