Miglustat hydrochloride is primarily used in the treatment of Gaucher disease type 1, a genetic disorder where the body cannot properly break down a certain type of fat. It works by inhibiting the enzyme responsible for the production of glucosylceramide, the fat that accumulates in the cells of affected individuals. This helps to reduce the storage of this substance and alleviates symptoms such as enlarged spleen and liver, bone abnormalities, and blood disorders. Additionally, it is sometimes prescribed for Niemann-Pick disease type C, another genetic condition affecting lipid metabolism, where it helps to slow disease progression and improve neurological symptoms. The drug is particularly beneficial for patients who cannot undergo enzyme replacement therapy.