Quinagolide hydrochloride is primarily used in the treatment of hyperprolactinemia, a condition characterized by abnormally high levels of prolactin in the blood. It works by acting as a dopamine receptor agonist, which helps to inhibit the secretion of prolactin from the pituitary gland. This makes it effective in managing symptoms associated with elevated prolactin levels, such as irregular menstrual cycles, infertility, and galactorrhea (unexpected milk production). Additionally, it is utilized in the treatment of prolactin-secreting pituitary adenomas, helping to reduce tumor size and control hormone levels. Its long-acting nature allows for once-daily dosing, improving patient compliance and convenience.