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.
In delayed and obstructed menstruation, when the discharge is scanty, dark, and of glutinous character, I have long prescribed the carbonate of magnesia with beneficial results, and especially when the irregularity is attended with sick headache and mental depression; it is most indicated in rheumatic subjects. Five to sixty or ninety grains may be given, according as to whether the constitutional, the laxative, or fully purgative action is required. The small dose should be given each night for the first fortnight after the cessation of the menses, and the larger doses during the latter fortnight, or especially before or during the period, or when headache and depression are present.