Amitriptyline is a medication that belongs to a class of medications called tricyclic antidepressants. It is used to treat mental/mood problems such as depression, anxiety, and tension. It works by affecting the balance of certain natural chemicals (neurotransmitters such as serotonin) in the brain. Amitriptyline is also used for some types of pain, including chronic pain syndrome, diabetic neuropathy, fibromyalgia, interstitial cystitis, and postherpetic neuralgia. It can help reduce pain, relax muscles, and improve sleep. Amitriptyline is available as tablets and as a liquid, and it is taken by mouth. It is usually taken at regular intervals, and it may take 1 to 2 weeks to start feeling better, but it can take 4 to 6 weeks for amitriptyline to work fully. Common side effects of amitriptyline include dry mouth, constipation, and drowsiness. It is important to talk to a doctor before taking amitriptyline, especially if you have any allergies, heart problems, liver problems, or are taking other medications.