Let’s say I’m vegan and I need to take vitamin B12 supplements to be healthy. Furthermore, let’s say I have ADHD, I forgot to take them for a month, I feel like shit, and while I know to take them now, there’s no guarantee I’ll remember tomorrow.
If I were to take 2 tablets today, an amount which I surely need, would my body actually absorb all the B12 it needs, or would I piss out the second tablet? Do I have to wait until tomorrow to absorb the nutrients my body needs now?
https://www.mayoclinic.org/drugs-supplements-vitamin-b12/art-20363663
When taken at appropriate doses, vitamin B-12 supplements are generally considered safe. While the recommended daily amount of vitamin B-12 for adults is 2.4 micrograms, higher doses have been found to be safe. Your body absorbs only as much as it needs, and any excess passes through your urine.
High doses of vitamin B-12, such as those used to treat a deficiency, might cause:
Emphasis mine.
To add to this: I went to the doctor after a nerve injury and asked whether taking B supplements would help with recovery. She said "no, No, NO please don’t take any extra B supplements because your levels are already fine. I’ve seen enough patients come with unexplained burning, tingling and twitching sensations in their bodies and it’s always because they take B supplements unnecessarily. So don’t even think about it "
So yes our bodies can filter a lot but even then it’s also possible to overdose. Doesn’t seem to be OPs case though.