For many years, virtually all pharmaceutical companies had an agrochemical division. This was partly to maximize the benefits of expensive chemical synthesis efforts by searching for many types of useful biological activities. Leads for pharmaceuticals and pesticides often overlap, in some cases leading to similar compounds used for human health and weed management purposes. This review will focus on herbicides and herbicide classes that have potential pharmaceutical properties, both as therapeutic agents that act through human molecular target sites and those that act on infectious agents. An example of the first case is compounds that target plant acetyl coenzyme A carboxylases, inhibiting fatty acid synthesis, and similar compounds used in humans as anti-inflammatory agents. Another such example is the triketone class of compounds that can act both as herbicides and as treatments for the genetic disease tyrosinemia, targeting the same enzyme in both cases. Examples of the second case are the relatively large number of herbicides that have activity against the malaria protozoan (Plasmodium spp.). It turns out that Plasmodium spp. and related disease organisms have an organelle that is apparently analogous to the plant plastid, the apicoplast. Herbicides such as dinitroanilines are active against several protozoan parasites by the same mechanism by which they kill plants, interaction with tubulin to halt cell division and other tubulin-dependent processes. These and other multiple activities of various herbicides and herbicide classes provide perspective on the broad biological activity of herbicides and related compounds.