Hi pinkblossom!
Yes, it sounds like the dosage is too high. Did it make you cough?
Ideally, it's best to buy a milligram scale so you can measure how much glutathione you're using.
They are about
$20 on amazon. You can find them under the search term "0.001g scale".
(make sure to double check the amount of zeros in that number, so you don't accidentally buy the wrong one)
4% of 20 grams is 800 mg. This is a bit too high so that could explain why. It's best to stay under 500 mg.
So in other words, only 1/40th of the entire bag of 20g.
Another thing you can try is to add a pinch of baking soda. It will lower how acidic it is.
The 1/2 tsp, was that a leveled teaspoon?
I have some glutathione powder that I can weight for you to get an idea.
I have a write up here which might help too:
https://www.healingwell.com/community/default.aspx?f=30&m=4337353