I did that experiment with my flatmates for some weeks once. (I love them, but they had it coming.)

One had a tighter schedule and you actually noticed the change pretty fast. I ended up telling him pretty early.

The other one didn’t notice at all, so I just went on and on. He was mad at me when I told him. Told me I should’ve just kept going if it’s working.

Both couldn’t tell from the taste alone.

From what I’ve heard you’d probably see a spike in medical deaths basically immediately.