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Side Effects of Tolcapone

Many people who take tolcapone may begin to develop significant and sometimes intolerable side effects over time. In fact, some side effects of tolcapone may be serious and require immediate medical attention. These serious side effects include high fever, severe diarrhea, or hallucinations. However, in many cases, the tolcapone side effects are minor and either require no treatment or are easily treated.

Side Effects of Tolcapone: An Overview

As with any medicine, side effects are possible with tolcapone (Tasmar®). If side effects do occur, they are often minor and either require no treatment or are easily treated by you or your healthcare provider. However, as with any levodopa therapy, many people will begin to experience significant and sometimes intolerable tolcapone side effects over time.
(This article covers many, but not all, of the possible side effects with tolcapone. Your healthcare provider can discuss a more complete list of tolcapone side effects with you.)

Serious Side Effects of Tolcapone

Some side effects with tolcapone 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. Again, many of these side effects may be due to carbidopa-levodopa, not tolcapone. These serious side effects of tolcapone (plus carbidopa-levodopa) include but are not limited to:
  • Any signs of liver damage, such as:
    • Elevated liver enzymes (found using a blood test)
    • Persistent, severe nausea
    • Severe fatigue or lethargy
    • Loss of appetite
    • Yellowing of the whites of the eyes or skin (jaundice)
    • Dark urine
    • Severe itching
    • Upper-right abdominal tenderness
  • Severe diarrhea
  • Severe muscle pain
  • Symptoms of neuroleptic malignant syndrome (NMS), which may occur if tolcapone 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)


  • Intense, unusual urges, such as urges to gamble or engage in risky sexual activity 
  • Low blood pressure (hypotension) or high blood pressure (hypertension)
  • Fainting
  • Falling asleep suddenly and without warning during the day
  • Falling
  • Bleeding in the digestive tract
  • Psychiatric problems, such as:
    • Hallucinations
    • Hostility
    • Delusions
    • Paranoia
    • Depression
  • Intestinal ulcers (known as duodenal ulcers)
  • A heart attack
  • Falling or balance problems
  • Signs of an allergic reaction, such as:
    • An unexplained rash
    • Hives
    • Itching
    • Swelling of the mouth or throat
    • Wheezing
    • Difficulty breathing.
The most serious side effect of tolcapone is liver failure. In order to help catch this side effect early, your healthcare provider will need to check your liver enzymes (using a simple blood test) every two to four weeks for the first six months. After that, your healthcare provider can check your liver enzymes periodically as necessary. If at any time your liver enzymes increase past twice the normal upper limit, you must stop taking tolcapone permanently.
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