I have a lot of experience with this and research background.
If the depressed feeling lasts for a few days then it's unlikely a herx. Glutathione gets used up quickly in the body. However, the detox process that glutathione uses relies on methyl-b12 and methyl-folate. If you are low in either of these, then increasing glutathione will deplete your B vitamin stores faster.
If you have MTHFR, MTRR, or MTR mutations in your genetics, then glutathione will make you feel worse, not better.
If you have access to them, try taking 1mg (1000mcg) Methyl-B12 and 1000mcg Methyl-folate. If they're sublingual then you must hold them in your mouth for at least 40 minutes for them to work. The best place is to put them is between your upper lip and gums. If you chew and swallow them, it won't work.
If you have MeB12 injections, take 1000mcg and then take the same amount of methyl-folate by mouth. If they aren't the methyl forms then they won't fix your depleted status.
If you feel better within hours of taking these, then your problem is that your body probably has the common genetic mutations in the methylation cycle or detox pathways and glutathione is burdening your body.
TL;DR version -- you're likely experiencing a deficiency state and glutathione makes you more deficient.
Thank you for this info. I very likely have this issue. My doc put me on liposomal glutathione in Sep 2016. I've taken it daily ever since. I have some problems with it. It often makes me feel worse, and there were many times I felt like my body was dumping toxins after taking it, as I would have to urinate soon after and would feel some pain with urination. I also suspect it's pulling mercury or other heavy metals as I increasingly feel like that is happening, too, but I'm afraid to stop taking it. I'm very toxic and an extremely poor detoxes.
I would love to test the B-12 and folate you mentioned, but I've been afraid of B-12 and multivitamins for years. I had allergy patch testing done in 2009 and tested positive for cobalt and chromium. B-12 has cobalt and multivitamins have both. I don't know if they would cause problems for me in reality or not. I did take cheap multivitamins years ago and never noticed anything, but I'm sure I could potentially cause inflammation or damage without any obvious reactions. I've looked at these in the store, but chickened out when I realized all the B vitamins were in the form of saccromyces cerevisea (bakers yeast). Also they're all in megadoses. Do you know of any brands that are not yeast based and are in low doses that might be safe for me to test?
My B-12 was tested in Sep 2016, and it was at low end of normal in the 200's range. If glutathione reduces B-12, I wonder what mine is now?!!!