I bought mine from inhousepharmacy.biz. I currently take it twice per day, 1 in the morning and one at night. I experimented with only one per day and 3 per day and for me 2 seems just right. I don't have what's thought of as sleep apnea, nor do am I using it for altitude adjustment both of which are legitimate reasons. Since I work in a hyper-oxygen environment and I do not think it is wise to expose ourselves to unnaturally high oxygen levels I am using it as protection against that. I spoke with Benedicte about this so I didn't just willy nilly decide to take it. I feel it has helped my body fluid regulation a lot and the improved venous tone seems to suggest that as well. I will continue to take it for a couple more months until I am done with my present job and then reevaluate. I'm sure a persons context would determine if it is a beneficial supplement for them. It shouldn't be taken in severe emphysema though because those people really do have an impaired ability to 'blow off' CO2 from loss of lung tissue elasticity. That's just an FYI, not a real common problem, but potentially for a few people. I'm a real fan of CO2 and feel optimizing it in my own body has paid off after living so long with impaired cellular respiration, some of which was my own doing and some was my environment.