Final answer:
Morphine is the analgesic commonly administered via transdermal patch for pain relief, used in both acute and chronic pain management without affecting consciousness at controlled doses. Therefore, the correct option is A.
Step-by-step explanation:
The drug that is an analgesic commonly administered via transdermal patch is Morphine. Morphine is a potent opioid pain medication that is often used before and after surgical procedures to alleviate severe pain. It is one of several opioids, including codeine and oxycodone, which are used to manage pain without significantly affecting consciousness. However, at higher doses, opioids like morphine can act as narcotics, inducing drowsiness and loss of consciousness. Opioids are part of a class of drugs that also includes illicit substances like heroin, as well as prescription pain relievers such as methadone and fentanyl. When administered through a transdermal patch, morphine provides continuous pain relief and is a convenient option for patients in need of long-term pain management.