if you stay at 40mcg honestly after 3 days you wont feel anything from the clen
thats why people up the dose every two days, by the end of the second week im at 120-160mcg, i think if you keep doing it you can get up to absurd dosage since the receptors are shot
albuterol is much better imo, you dont get used to it nearly as fast as clen, feels stronger to me
i like to do albuterol 3 days a week coupled with coffee/caffeine