Yes, I am on guanfacine. I now have high blood pressure as a result of my initial Covid infection in March 2020. My cardiologist prescribed Telmisartan. This past year, however, my research has found that guanfacine, which is used to treat high blood pressure, is also used to treat ADHD. Long Covid researchers have found that guanfacine combined with NAC (N-Acetyl Cysteine) helps with brain fog.
I had my PCP switch me to guanfacine for my high BP, and then got over-the-counter NAC (600mg). I have found that my general day-to-day brain fog has improved, but the brain fog I experience while in a crash/flair up seems to be the same.
Here is the article I sent to my PCP for the guanfacine prescription:

Yale School of Medicine: “Potential New Treatment for ‘Brain Fog’ in Long COVID Patients”
December 13, 2022
https://medicine.yale.edu/news-article/potential-new-treatment-for-brain-fog-in-long-covid-patients/
Note: I did this gradually starting with 1mg guanfacine per day for one month and then going up to my current dose of 2mg. After another month, I began 300mg of NAC and then went up to the full 600mg after an additional month.