@Oliver3 The drug is diamox. Paul Cheney would occasionally prescribe it to some of his ME patients, finding that it symptomatically seemed to relieve chronic pressure headaches in some cases.
Interestingly, as part of his annual clinical exam, Cheney would have his ME patients fully exhale and then hold their breath for 30 seconds, measuring their oxygen saturation levels with a finger pulse oximeter. He found that all of his patients had normal (98-99%) oxygen saturation prior to breath hold, but that many of them would barely desaturate after breath hold - dropping only a few percent.
He prescribed diamox to me in the mid-2000s and while I was on it, he noted that my oxygen desaturation improved substantially, dropping by ~15% during breath hold, compared to only 5-6% pre-diamox. I think my exercise capacity improved while I was on diamox, though that was a long time ago. In contrast, mestinon worsened my exercise intolerance during a 3-month trial of it, even though my iCPET by David Systrom showed me to be in the “high-flow” subset of ME patients who often clinically benefit from mestinon.
After the Naviaux paper on metabolomics in ME patients was published, Cheney adopted the view that ME is probably a protective metabolic state, that we have switched from aerobic to anaerobic metabolism because we are deficient in antioxidant defenses. He found that his patients had abnormally low levels of SOD, catalase, and glutathione synthase. Strangely, he found that a 6-day course of artesunate - the anti-malarial drug - increased SOD and catalase to normal levels in his ME patients, which is why he recommended it for a while.
Cheney eventually stopped prescribing diamox because he feared greater oxygen desaturation also increased aerobic metabolism, and with it the production of dangerous reactive oxygen species, though he never tested this theory. I have occasionally toyed with the idea of trying diamox again, especially since my muscle fatigability has become so disabling in recent years.