This section is from the book "Materia Medica And Therapeutics - Vegetable Kingdom", by Charles D. F. Phillips. Also available from Amazon: Materia Medica And Therapeutics: Vegetable Kingdom.
The juniper and its dark purple fruits are well known, and need no description, especially as the medicinal uses are very limited.
As regards its employment in pharmacy, very little that is useful can be said. It was formerly given extensively as a diuretic, sudorific, and carminative, but is by no means so innocent a diuretic that it may be used recklessly. In acute and subacute nephritis, and in the nephritis of scarlatina, juniper has often aggravated the mischief. Given in excess, it has also produced much irritation of the bladder and urethra. As a diaphoretic, it has occasionally been substituted for guaiacum.
The active ingredient is an ethereal oil, obtained from the berries and the young tops, that from the latter being considered the best. (A tar obtained from juniper wood by distillation and called in pharmacy oil of cade ( Oleum Cadini), is much used as a local application in cutaneous diseases. It may also be given internally.)