Which of the following is true about Medicare Plan D?

Medicare Plan D is a prescription drug coverage plan that provides beneficiaries with assistance in paying for their medications. The correct statement indicates that insurance companies can limit prescriptions to 30-day supplies. This reflects the flexibility insurance plans have in managing their formulary and the distribution of medications. Many plans implement such limits as a means of controlling costs, ensuring adherence, and managing inventory effectively.

In practice, beneficiaries may find that some medications can be prescribed for longer durations, but insurers often opt for a lower supply limit to ensure regular interactions with healthcare providers and to mitigate potential misuse of medications. This practice also allows insurers to manage prescription drug benefits more effectively by putting a system in place where ongoing patient assessments can occur.

The other options do not accurately reflect how Medicare Plan D operates: it is not mandatory, it does not cover all medications without restrictions, and there are typically costs associated with enrollment in the plan, including premiums and potential deductibles.