*mental health clinic. Had to edit that type-o.
Do they need to be taken together for positive effect or would taking one (say milk thistle) in isolation still be beneficial?
You could try one at a time, sure! May be good to see what helps and doesn't do much. Supplements also typically take 2-3 months to work to full benefit, but you should see subtle signs of their effects sooner.
I’ve heard St. John’s wort can help lift some ocd and depression symptoms
That is also true! St. John's Wort has more health side effects and you have to be careful what you mix it with, from what I've heard
St. John’s wort can interfere with hormonal birth control so be careful!