Meperidine is an opioid that can be administered intravenously to provide sedation, anxiolysis, and analgesia during labor. It provides pain relief that is superior to nitrous oxide but inferior to regional anesthesia.

promethazine is an antihistamine that can be used as an adjunct to opioids to enhance their analgesic effect and reduce nausea and vomiting, but it does not provide analgesia by itself.

diazepam is a benzodiazepine that can be used as a tranquillizer to alleviate anxiety and increase patients’ acceptance of labor, but it does not provide analgesia by itself.

nitrous oxide is an inhaled anesthetic agent that can be self-administered by the patient to provide some form of noninvasive pharmacologic pain relief, but it is less effective than opioids or regional anesthesia. It also has a negative environmental impact as a greenhouse gas.