The correct answer is: They include both patented and off-patent drugs. This statement is incorrect in the context of essential medicines.

Essential medicines are those that satisfy the priority health care needs of the population.

They are selected based on several key criteria:
- Priority Health Needs: Medicines are chosen according to the most pressing health challenges faced by the community or country, ensuring relevance and impact.
- Effectiveness and Safety: The selected medicines must have well-established efficacy and safety profiles.
- Affordability and Accessibility: To maximize public health benefits, essential medicines should be affordable and available at all times and in adequate amounts.
- Typically Off-Patent: Essential medicines generally consist of drugs that are off-patent, which allows for generic production and lower cost. Including patented medicines contradicts the goal of affordability and accessibility.

Therefore, the inclusion of patented medicines in the essential medicines list is generally avoided because patents can limit the availability of low-cost generic alternatives, raising costs and hindering wide access.

In summary: Essential medicines are carefully selected, mostly off-patent, affordable drugs that address priority health needs, ensuring safe and effective therapies are available to populations.

Reference: WHO Model List of Essential Medicines, 23rd Edition, 2023