Acid Phos is indicated for nervous exhaustion, mental debility, apathetic. It is also used for falling of the hair, somnolency, young people who are overtaxed mentally or physically have been exposed to the ravages of acute diseases, grief, loss of vital fluids, and useful in relieving pain of cancer. It is reported to be useful in cases of premature grey hair and hair fall (3x and higher). It is also used with success in both diabetes insipidus and mellitus.

Reference

1. W. Boericke, New Manual of Homoeopathic Materia Medica & Repertory [with Relationship of Remedies], Second Re-Augmented & Revised Edition Based on Ninth Edition, Reprint Edition 2002.
2. Dr. P. N. Varma, et al., A Compendium of Rare and Clinically Established Mother Tinctures, 4th Edition.