system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can alcohol really effect individuals differently at higher elevations? What about THC in marijuana?
gpt
Alcohol yes, if you are not used to the elevation. Alcohol does lower blood oxygen saturation, which means that less oxygen is being carried to tissues throughout the body. High elevation does the same thing because there is less oxygen in the atmosphere. Drinking at high elevations would combine both of these effects. This would only occur within the first couple days of being at a higher elevation since the body will recognize that there is less oxygen available in the atmosphere and generate more red blood cells in order to compensate. People who live at high elevations will not be affected by this, but may have the opposite effect when going to lower elevations. 

THC no, because its affects have nothing to do with the cardiovascular or respiratory system, beyond the actual smoking of it. The change in atmospheric pressure is not likely to have much of any effect on the absorption of THC in the lungs.