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Side Effects of Entacapone
Abdominal pain, nausea, and involuntary body movements are some of the most common side effects of entacapone. If side effects occur, they are usually minor and either do not require medical attention or can be treated easily. However, some people may begin to experience significant and sometimes intolerable side effects over time. Potentially serious entacapone side effects include malignant melanoma, psychiatric problems, and intestinal ulcers.
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As with any medicine, side effects are possible with entacapone (Comtan®). If side effects do occur, they are often minor and either require no treatment or can be treated easily by you or your healthcare provider. However, as with any levodopa therapy, many people will begin to experience significant and sometimes intolerable entacapone side effects over time.
(This article covers many, but not all, of the possible side effects with entacapone. Your healthcare provider can discuss a more complete list of entacapone side effects with you.)
Some side effects of entacapone are potentially serious and should be reported immediately to your healthcare provider. Although most of these serious side effects are rare, a few may be common. Many of these side effects have occurred with carbidopa-levodopa products, which have been available for a long time, and are expected to also be a problem with entacapone, since entacapone is always taken with carbidopa-levodopa and since entacapone increases the level of levodopa in the blood. These serious side effects of entacapone (plus carbidopa-levodopa) include but are not limited to:
- Severe diarrhea
- Severe muscle pain
- Intense, unusual urges, such as urges to gamble or engage in risky sexual activity
- Symptoms of neuroleptic malignant syndrome (NMS), which may occur if entacapone is stopped too abruptly, such as:
- A high fever
- Stiff muscles
- Confusion
- Irregular pulse or blood pressure
- A fast heart rate (tachycardia)
- Sweating
- Irregular heart rhythms (arrhythmias)
- Low blood pressure (hypotension) or high blood pressure (hypertension)
- Fainting
- Bleeding in the digestive tract
- Psychiatric problems, such as:
- Hallucinations
- Delusions
- Paranoia
- Agitation
- Anxiety
- Depression
- Suicidal thoughts or behaviors
- Intestinal ulcers (known as duodenal ulcers)
- Low white blood cell, red blood cell, or blood platelet counts
- Seizures
- Heart attack
- Malignant melanoma (a type of skin cancer)
- A painful penile erection that does not go away (known as priapism)
- Falling or balance problems
- Signs of an allergic reaction, including:
- An unexplained rash
- Hives
- Itching
- Swelling of the mouth or throat
- Wheezing
- Difficulty breathing.
Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD



