Neostigmine methyl sulfate is primarily used in the medical field to treat myasthenia gravis, a condition characterized by muscle weakness. It works by improving muscle strength through the inhibition of acetylcholinesterase, an enzyme that breaks down acetylcholine, thereby increasing the levels of this neurotransmitter at the neuromuscular junction. This action helps to enhance communication between nerves and muscles, leading to improved muscle function.

Additionally, it is employed in the reversal of non-depolarizing neuromuscular blockade after surgery. Anesthesiologists administer it to counteract the effects of muscle relaxants used during surgical procedures, facilitating the recovery of normal muscle activity and ensuring the patient can breathe independently post-operation.

In some cases, it is also used to manage urinary retention or paralytic ileus by stimulating the smooth muscles of the bladder and gastrointestinal tract, promoting normal function. Its ability to enhance cholinergic activity makes it a valuable therapeutic agent in these clinical scenarios.