Most of the known risks associated with amitriptyline are linked to its use in treating depression. Doses to treat fibromyalgia are usually much lower, which in theory should reduce the severity and risk of side effects. Still, anyone taking the drug should be aware of these potential risks:
Suicidal thinking and behavior. Antidepressants including amitriptyline may increase this risk in children, adolescents, and young adults who have major depression or another mental illnesses. The drug actually has a "black box" warning from the Food and Drug Administration—the strongest warning of its kind—about this risk. Call a doctor if you notice new or worsening depression, extreme worry, agitation, panic attacks, irritability, or thoughts of self-harm.
Cardiovascular problems. These include irregular heartbeats (arrhythmias), heart attacks, and strokes. Use the drug with extreme caution if you have a history of heart disease, and don't take it at all if you've had a recent heart attack.
Dizziness and drowsiness. The drug has a sedating effect, so don't drive until you know how it affects you. Certain antihistamines, sleeping pills, and muscle relaxants can increase that sedating effect. Alcohol should not be consumed while taking this medication, since it might also increase sedation as well as the possibility of a suicide attempt or overdose.
Dangerously low blood pressure. That can cause dizziness, lightheadedness, or fainting when you get up quickly from a lying position. So get out of bed slowly, resting your feet on the floor for a few minutes before standing.
Withdrawal symptoms. If you want to stop taking amitriptyline, talk with your doctor, who can reduce your dose gradually over several weeks to reduce this risk.
Toxicity. A toxic dose of amitriptyline varies considerably among individuals and can cause life-threatening reactions, so dosages should start low and be increased slowly. But because lower doses are generally used to treat fibromyalgia anyway, there is less risk a person would experience these side effects. Nevertheless, patients—especially children, older people, and those with heart disease—should be monitored for abnormal heart rhythms (arrhythmias), high fever, agitation, confusion, excessively low blood pressure (hypotension), hallucinations, irritability, muscle rigidity, and seizures.
Other side effects. Fibromyalgia patients treated with amitriptyline in clinical trials have reported dry mouth, constipation, headaches, nausea, rashes, sleepiness, sweating, urinary retention, vomiting, and weight gain.
Drug interactions. Don't use amitriptyline if you are taking or have recently taken a monoamine oxidase (MAO) inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), selegiline (Eldepryl, Emsam, Zelapar), and tranylcypromine (Parnate). Because amitriptyline interacts with many drugs, tell your doctor about all prescription and nonprescription medications you are taking.
Disease interactions. Amitriptyline can worsen certain conditions, including bipolar disorder, enlarged prostate, glaucoma, liver disease, overactive thyroid, schizophrenia, seizures, and urinary difficulties. The drug also might cause problems in a fetus or infant, so it shouldn't be taken by pregnant women or those who are breast-feeding except in extreme cases.