Final answer:
The nurse should explain to the client that antidepressants often take several weeks to be fully effective.
Step-by-step explanation:
The nurse should explain to the client that antidepressants often take several weeks to be fully effective. Antidepressant medications, such as citalopram, need time to build up in the body and regulate the levels of neurotransmitters in the brain. The client's improved appetite suggests that the medication is having some effect, but it may take longer for the medication to fully alleviate symptoms of depression and sleep problems. It is important for the nurse to provide support and reassurance to the client during this time and encourage them to continue taking the medication as prescribed.