A mechanism of action (MoA) diagram shows where a drug acts and what happens next. It is one of the most common figures in pharmacy and pharmacology theses.
Decide whether you show the whole body, an organ, a cell or a single receptor. Mixing levels makes the figure confusing; use an inset if you need two.
Show the cell membrane, cytoplasm and nucleus (or the relevant tissue) as background areas. Put each molecule in the right place.
Give the drug one strong colour and keep everything else calmer, so the reader's eye goes to the drug and its target first.
End the pathway with the clinical effect, for example “↓ blood glucose”.
Try the Mechanism of Action Diagram Maker: type “mechanism of action of metformin” and refine the result.