I am on medicine for hypothyroidism. My thyroid levels were checked many times over the years but didn't test as abnormal until about 3 years ago. I'm on medicine for that, and was told it might also help with my depression, but honestly I never noticed a difference.

Two or three times my vitamin D levels have tested as low and I was put on prescription-level vitamins for a time. I did not really see a difference then either.

I'm assuming that even if the treatments didn't make me feel better, maybe not having the treatments would have made me feel worse? In any case, even if it doesn't affect my depression, it's important for my physical health that these things are in check, especially my thyroid.