Thank you for your answers.
I get a burning sensation in the stomach immediately after taking DMSA and later pain. Since the reaction is so immediate, I guess it is caused when the DMSA is absorbed in the stomach. Same thing if I try to eat raw onion.

When I take the DMSA, I open the gelatin capsules in order to control the dose. Will the capsule somehow affect the absorption?
For example where it is absorbed.

I have been on a low carb diet for a long time (9 months) but perhaps I can try to impove it further.
I will try molbdenium to see if it helps.