The Selegiline Hydrochloride segmentation by application delineates four principal therapeutic domains that collectively drive market revenue. Parkinson's disease remains the dominant segment, accounting for roughly 55 % of total sales, as selegiline is approved as an adjunct to levodopa therapy and commands a stable, long‑term prescribing base. Major depressive disorder contributes about 30 % of the market; the drug’s monoamine‑oxidase‑B inhibition offers a distinct mechanism that supports its use in treatment‑resistant cases, leading to higher per‑patient pricing. Cognitive disorders, including early‑stage Alzheimer's and mild cognitive impairment, represent an emerging niche of 10 %, reflecting ongoing clinical trials and off‑label adoption that gradually expand the addressable population. The residual 5 % is captured by off‑label/other indications such as fatigue and smoking cessation, where limited but growing demand adds incremental volume. Together, these application categories define the overall market size, with each segment’s growth trajectory influencing production planning, pricing strategy, and investment in regulatory pathways.