Protriptyline hydrochloride is primarily used in the treatment of depression, particularly for individuals who experience low energy and fatigue as part of their depressive symptoms. It works by increasing the levels of certain neurotransmitters in the brain, which helps improve mood and energy levels. Additionally, it is sometimes prescribed for managing attention deficit hyperactivity disorder (ADHD) in adults, as it can enhance focus and reduce impulsivity. In some cases, it is also utilized to treat chronic pain conditions, such as neuropathic pain, due to its ability to modulate pain signals in the nervous system. It is typically administered orally and requires careful dosage adjustments to minimize side effects.