At first it simply blocked physically-induced PEM (I still had cerebrally-induced PEM). After a year or two, I tried going without cumin, to see if it was still being effective. Well, I've done lots of physical exertion since then, and never had PEM from it, so I think that counts as cured. I still have other ME symptoms such as mental lethargy, so my ME definitely isn't cured, but getting rid of PEM from physical activity sure is nice.
See this thread for details:
https://forums.phoenixrising.me/threads/cumin-cuminum-cynimum-possible-pem-blocker.56232/
If you try it and it works for you, please let me know. It's hard to believe that I'm the only PWME that it would work on.