Selegiline is primarily used in the treatment of Parkinson's disease. It works by inhibiting the breakdown of dopamine in the brain, helping to maintain higher levels of this neurotransmitter, which is crucial for motor control and coordination. This can alleviate symptoms such as tremors, stiffness, and slow movement.

In addition to its use in Parkinson's disease, selegiline is also employed in the treatment of major depressive disorder, particularly in cases where other antidepressants have not been effective. It functions as a monoamine oxidase inhibitor (MAOI), which helps to increase the levels of certain chemicals in the brain that are associated with mood regulation.

Selegiline is available in various forms, including oral tablets and transdermal patches. The transdermal patch is specifically used for depression and offers the advantage of bypassing the digestive system, reducing the risk of certain side effects.

Beyond its medical applications, selegiline has been explored for its potential neuroprotective effects, which could be beneficial in slowing the progression of neurodegenerative diseases. However, this application is still under investigation and not yet widely adopted in clinical practice.

Additionally, selegiline has been studied for its potential role in reducing cigarette cravings to aid smoking cessation, though this is not a primary or approved indication.