Which of the following signifies a prescription requirement for a drug post-marketed?

The indication "For prescription use only" is significant because it clearly communicates that the drug is intended to be dispensed only with a valid prescription from a licensed healthcare provider. This label indicates that the drug has been evaluated and determined to require a healthcare professional's oversight for safe and effective use, often due to its potential for misuse, side effects, or necessity for monitoring.

In contrast, the other options suggest different levels of accessibility or usage but do not imply a requirement for a prescription. "Available by pharmacy only" might suggest distribution limitations, but it does not specify the need for a prescription. "General consumption approved" and "Approved for non-prescription use" clearly indicate that the drug can be purchased without a prescription, which is not relevant to prescription requirements. Therefore, the first label best signifies the necessity of a prescription for the drug in question.