Cholinesterase inhibitors are a class of medications that block the action of the enzyme cholinesterase, which breaks down the neurotransmitter acetylcholine. By preventing this breakdown, these drugs increase the levels of acetylcholine in the brain, which can help improve communication between nerve cells. They are primarily used to treat conditions like Alzheimer's disease and other forms of dementia. These medications can enhance cognitive function and slow the progression of symptoms in some patients. Common examples of cholinesterase inhibitors include donepezil, rivastigmine, and galantamine. While they can be beneficial, they may also cause side effects such as nausea, diarrhea, and insomnia.