Final answer:
The missing mandatory requirement from the prescription is likely the prescription date, which is essential for the validity and tracking of the medication prescribed.
Step-by-step explanation:
The missing information from the prescription, which is a mandatory requirement under laws regulating monitored drugs, would likely be a) Prescription date. Prescription details typically must include the date the prescription was written, as this is essential for determining its validity period and for the pharmacy to track when the medication was prescribed.
The dosage information is usually a part of the prescription as well, but since this is a hypothetical scenario, it is assumed that the dosage might already be specified with the medication name (Tylenol #3) itself. Additionally, the expiry date of the medication and the pharmacy contact details are important but are not necessarily a part of the prescription; they are typically managed by the pharmacy upon dispensing the medication.