Spirulina. I dilute 1 flat table spoon of powder with 1 cup of water, and take this twice per day. The taste is not good but it is tolerable knowing that it is a vegan superfood hence good for me.
Today I had to stop. After using it for some 3 weeks without any adverse events, in about week 4 I may have served myself a slight overdose; about 1 heaped tablespoon with a cup of water. Shortly thereafter I felt some nausea, but was not sure if it was from the spirulina or other foods that I followed it up with, a bad combo, or a contamination. Today, in about week 5 of the trial, I made myself a dilute serving, a teaspoon to 1 cup of water. I had two sips and got immediate nausea, and stopped.
There does not seem to be spirulina intolerance on google, but there are adverse reactions reported.
I'm not sure at all that I factored out everything, but I'm taking a break from it. I've never hit such a hard limit on a food.