Let your boss know that you need a job that lets you better address your mental health with this resignation letter concerning depression.
January 25, 2018
Dear (Employer Name),
It is with great regret that I tender my resignation, effective (date). I have enjoyed my (amount of time) here at (Company), and I am grateful for the opportunity to expand my understanding and skill in (field). However, the (aspect) of my role has had a negative effect on my depression, and I will be departing to find work that helps me manage my mental health more effectively.
Thank you for all you've done for me, and best of luck in the future.