The pharmacy modules exist because dispensing carries obligations an ordinary shop does not have: you must be able to say what you gave to whom, from which batch, and when it expires.
Prescriptions
Record the prescription, then reference its ID at the till when you dispense. The till has a Prescription ID field for exactly this, so the sale and the prescription are linked rather than sitting in two unrelated places.
Drug register
The controlled-drugs register. A manager can read it for oversight; recording entries needs full pharmacy rights, which is the Pharmacist role.
Batch tracking and expiry
Batches come in through purchase orders — enter the batch number and expiry as you raise the order. Expiry Tracking then shows what is approaching its date, and the dashboard surfaces this month. Stock is drawn from batches as you sell, so the register reflects which batch actually went out.
Expiry tracking is only as good as the batch data entered at receiving. Skip it on a purchase order and those units are invisible to every expiry warning.