The simplest diagram is Manufacturer → Distributor → Pharmacy → Patient. It is useful, but reality quickly becomes more interesting.
Manufacturing is distributed
A drug substance may be produced in one country, formulated in another, packaged somewhere else, and stored by a 3PL before commercial distribution begins.
Possession and ownership can diverge
A 3PL may have physical custody without owning the product. A wholesaler typically buys and resells it. That distinction changes the commercial relationship, the records, and the risks each party manages.
Modality changes the route
A tablet, biologic, vaccine, and autologous cell therapy cannot share one universal supply-chain design. Temperature, shelf life, patient identity, and manufacturing model change what is possible.