Most people start to feel the effects of elevation at 8 -9k ft and some people are more sensitive than others Because this hike goes from 8314' ft at Whitney Portal all the way up to 14,505' at the Whitney summit EVEN IF you acclimate at elevation for a few days you might still get altitude sickness because you are gaining a lot of elevation very quickly 6600' in a day or two SO a lot of people will take a drug called Diamox to combat the effects of altitude sickness or even as a preventative measure The thing is and the reason why I didn't take any the side effects of Diamox are pretty much the symptoms of altitude sickness