Since the beginning of time, humans have searched for ways to ease pain, the sensation of suffering or distress. Even though pain is unpleasant, it is an essential feeling; its purpose is to let the body know that something is wrong. Despite this merit, pain can be difficult to endure for long periods of time. Most of the work of early medical practitioners was simply directed at ending pain, and any effective drug was prized. Today, pain is still feared and avoided, and hundreds of medicines and treatments have been developed to treat and prevent it.

There are many classes of drugs used by the medical community to treat pain. Some of the most effective painkillers have limited usefulness because they knock the patient unconscious.

Analgesics, drugs that can ease pain without causing unconsciousness, are valued because they...