This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Besides the astringent power exerted by 5 to 10-gr. doses of alum, we must notice the irritant effect of larger quantities, by which probably they become useful in constipation. Alum is seldom to be preferred to other remedies for this disorder, though it may act favorably in atonic cases, when the muscular coat of the bowel is deficient in power, and when mucous secretion is scanty. Mr. Aldridge has published reports illustrating the good effect of 20 to 40 gr. daily in producing copious and solid evacuations; he also associated it with sulphate of magnesia (Braithwaite, vol. xii.). Such treatment, however, is rarely worth trial, and my own experience with it is not favorable; it either in--creased constipation or caused dysenteric symptoms.