Which opioids are known for their analgesic properties?

The correct choice is associated with the well-documented analgesic properties of both heroin and morphine. These substances are classified as opioids, which are primarily known for their ability to bind to specific receptors in the brain and reduce the perception of pain. Morphine, for example, is often used in clinical settings as a potent pain reliever, especially for severe pain. Heroin, while illegal in many places, is derived from morphine and also possesses strong analgesic effects.

In contrast, the other options either include non-opioids or miss significant opioid representatives. Codeine does have analgesic properties but is much less potent compared to heroin and morphine. Caffeine is a stimulant and does not primarily function as an analgesic. Fentanyl is also a potent opioid, but aspirin is not; rather, it's classified as a non-steroidal anti-inflammatory drug (NSAID). Similarly, ibuprofen and acetaminophen do not belong to the opioid category; they are common over-the-counter medications utilized for mild to moderate pain relief, functioning through different mechanisms. Therefore, the selection of heroin and morphine highlights the classical and recognized nature of strong opioid analgesics.