The only supplement I take nowadays, is a multi-vitamin, and I choose a small pill because I have HUGE piles of prescription pills to take. The only other is an iron supplement, and only during my menstrual periods, since they are heavy.

I went through an approximate three year phase where I took oodles of OTC supplements, for various reasons. The only noticeable effect was distress from taking so darned many pills. I had to buy bigger pill boxes and a third pill box in order to even handle all of them. I will say here that if a doctor discovered that I had a deficiency, or if they recommended a prescription supplement (once I did have a prescription iron supplement), I would take it/them. But none are recommended beyond the two I mentioned.

If I recall correctly, during that 3-year period I took the following, plus a much bigger "horse pill" multi-vitamin:

• OTC Fish Oil - I took almost the maximum recommended. I actually took it more to lower my triglycerides, which it didn't help at all. It did nothing to improve my moods. I've been told that prescription fish oil is more effective, but not for everyone. Nowadays, I try to incorporate wild caught salmon and tuna into my diet as much as possible, as well as other sources of Omega 3s (flaxseed meal, chia seeds, walnuts). Tastes much better!
• Vitamin B Complex - I took it to increase my energy. Did not help.
• Zinc, Biotin, & Selenium - Took to help counter Lithium hair loss. Did nothing. Oddly, my hair loss finally eased AFTER I went off of these.

Oh, one advantage I did have was learning to swallow 10 or more pills at the very same time with one gulp of water.

Luckily, even my prescription pill numbers have gone down over the last five years. That's a good thing!