"Happiness is a choice. You just need to change your mindset and focus on the positive."
When you say this to someone struggling with depression, you are essentially telling them that they are CHOOSING to be sad… that they are bringing this depression on themselves. If it was as simple as choosing to be happy, don’t you think they would?
"You don’t need medication."
Unless you are a doctor, DO NOT give clinical or medical advice. Leave that to the professionals. Rather, encourage someone facing depression to talk it over with their doctor, and do not judge them if they follow their doctor's advice to try medication.
"You’re depressed again?"
They are already scared to be falling into depression again. Part of that fear is that they're becoming a burden to their loved ones. For you to sound annoyed does not help assuage their worries.
"Are you reading your Bible enough? Are you praying enough?"
To someone who is depressed, asking them this question feels as if you are saying, “If you just trusted God more or had more faith, you wouldn’t be depressed." As if somehow you're suggesting it is their fault God hasn’t healed them or that God acts based on our behavior. However, none of us can "DO ENOUGH" to make God act how we think He should. Thankfully, God’s love and provision are not based on our performance. God’s ways are wiser than ours, and He loves us like crazy. Instead, remind your friend that God is a healer, a refuge, and never gives up fighting for those who are in pain.