Pallegra is the kind of disease that shows up after a long period of time. It usually is the result of dietary deficiencies. By the time the patient gets around to complaining about it, the amount of niacin in the diet will likely not be enough. He is going to have to go to oral or intervenious treatment.
If that is the case, what he is most concerned about is how much he can take. Niacin does have side effects when you take too much of it and though not all that harmful, they can be very uncomfortable.
How much to take should always be a decision made by a qualified physician. Max should never self medicate. To get immediate results, a doctor will likely reference the Estimated Maximum value and cut it back some.