this following text is from the klenner protocol. in the era it was written, it was not yet known that polyunsaturated fatty acid deficiency prevent a successful niacin flush (which is why we all take fish oil now, which is absent from the klenner protocol - as is vitamin d3).
2) Niacin (nicotinic acid): We recommend 100mg to 3 grams, thirty minutes before meals and at bed hour, and also during the night if awake – whichever dose will produce a strong body flush. Niacin dilates the blood vessels, even those that have been compressed by scar tissue, allowing a greater amount of nutrient material to reach the cell laboratory or factor comprising muscles and nerves. This constant, repeated dilatation of the blood vessels acts in the same manner as the dilating urethral catheter to correct constriction. One is chemical, the other is mechanical. Hot fluids taken at the same time as the niacin will enhance the flush. Pyridoxine has been a suggested stimulant. The lack of constant flushing in Multiple Sclerosis is disappointing but not hopeless. It will require a longer time to achieve results. Many times patients will flush with intramuscular niacin when they fail to flush by the oral route. An occasional patient will experience the sensation of a chill following nicotinic acid flush. This is transient and of no consequence. Food, even jelly beans or a glass of milk, will prevent or minimize the experience. Some patients will flush sometimes and not at other times, even during a single day. If no flush develops within 45 minutes, the dose should be repeated. A delayed reaction of several hours can occur, and should this be superimposed upon a previous medication, the result could be severe. Do not scratch when itching from niacin. Just press the area with your fingers, or better still, with a cube of ice. Antihistamines will stop the itching and limit the flush, should this be necessary. Niacin should be given very slowly by the intravenous route in the geriatric patient, with or without cardiac pathology, since it can produce dilatation great enough to effect right-side heart failure. Myasthenia Gravis patients sometimes attain geriatric status. Vasomotor collapse of peripheral vessels, although rare, can occur. Eight mg. Decadron given IM will reverse this condition.