Selegiline HCl 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 lead to improved movement and reduced symptoms such as tremors, stiffness, and slowness of movement. In addition to its use in Parkinson's, it is also employed as an adjunct therapy in the treatment of major depressive disorder. By inhibiting monoamine oxidase B (MAO-B), it helps to increase the levels of certain chemicals in the brain that are associated with mood regulation, potentially alleviating symptoms of depression. Another application of Selegiline HCl is in the form of a transdermal patch, which is used for the treatment of major depressive disorder. This method of delivery allows for a controlled release of the medication, reducing the risk of certain side effects associated with oral administration. It is also sometimes used off-label for cognitive enhancement and in the treatment of certain neurodegenerative conditions, although these uses are not as well-established and require further research for validation.