Final answer:
The prescription abbreviation for "as the occasion arises; when necessary; as needed" is PRN, which stands for the Latin phrase "pro re nata."
Step-by-step explanation:
The prescription abbreviation for "as the occasion arises; when necessary; as needed" is PRN. This abbreviation is derived from the Latin phrase "pro re nata," which translates to "as the matter arises." PRN is commonly used in medical prescriptions to indicate that a medication should be taken only when needed. For example, if a patient is experiencing pain, they may be instructed to take a pain medication 'PRN'. It is commonly used in medical prescriptions to indicate that a medication should be taken only when needed for a specific symptom or condition, but not on a regular schedule. For example, a doctor might write a prescription for a pain reliever to be taken PRN for post-surgical pain, meaning the patient should only take the medication when they are experiencing pain.