Final answer:
Respiratory depression and sedation are the least frequent but serious adverse reactions of Morphine compared to common side effects like nausea and vomiting or constipation.
Step-by-step explanation:
The least frequent adverse reactions of Morphine, among the options provided, are likely respiratory depression and sedation. These adverse effects are indeed serious but tend to occur less frequently compared to common side effects such as nausea and vomiting or constipation. Morphine is an opioid analgesic that provides pain relief and can induce drowsiness or loss of consciousness at higher dosages, which is when sedation becomes more evident.
The dangerous effect of respiratory depression is of particular concern and may require intervention with an opiate antagonist like Naloxone, which is used to reverse this condition specifically in cases of opioid overdose or in newborns with narcotic-induced respiratory depression. Regular opioid use can also lead to tolerance and physical dependence, with withdrawal symptoms manifesting when the drug use is reduced or stopped.