I've had prescriptions for Diamox and carried it three times, but only for big peaks. Never for anything as moderate as Mount Whitney. Although Diamox does give most hikers some extra degree of safety against AMS, it is mostly unnecessary for Mount Whitney unless you suspect that you are susceptible to AMS.
Diamox has its own set of side effects. If you know them and recognize them, then they might not upset you. However, they bother some people, and the anxiety can be defeating. The side effects tend to worsen with the dosage and duration that you take it.
From the time that you first start taking Diamox, it takes two to three days for your body to attain a new water balance point, so it probably is unwise to start taking Diamox on the very day that you expect to climb. I once started taking Diamox at a half-dosage, let that run for 48 hours, and then increased to the standard dosage. Some people are allergic to it, so you would like to know that before you get in too deep.
When climbing a big peak one time, I felt good, so I wasn't taking any Diamox that I carried. The trip leader got desperate, so I gave him half of the Diamox that I had, and he was distributing it to others who had none. However, they were taking those pills without sufficient drinking water, and that is just plain silly.
