Pilocarpine HCl is primarily used in ophthalmology to treat conditions like glaucoma and ocular hypertension. It works by reducing intraocular pressure, helping to prevent damage to the optic nerve. Additionally, it is employed to counteract the effects of certain medications that cause pupil dilation during eye examinations. In some cases, it is also used to manage symptoms of dry mouth associated with conditions like Sjögren's syndrome or radiation therapy. Its ability to stimulate salivary and sweat glands makes it useful in these therapeutic applications.