Final answer:
The best indication that the morphine has been effective is decreased pain intensity.
Step-by-step explanation:
The best indication that the morphine has been effective is decreased pain intensity. Morphine is an analgesic and narcotic drug that is used to relieve severe pain. When the pain intensity decreases after taking morphine, it indicates that the medication is effective in reducing the pain.
Increased respiratory rate or improved appetite are not specific indications of effective pain relief. Decreased blood pressure and increased blood volume are not necessarily related to the effectiveness of morphine in pain relief.