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Demser Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 5/6/2016

Demser (metyrosine) prevents the tumor from making certain natural substances (catecholamines) that raise the blood pressure and make the heart beat faster and is given before surgery to control pheochromocytoma (tumor of the adrenal gland), and is also given when surgery is not possible. Common side effects of Demser include:

  • drowsiness
  • tiredness
  • dizziness
  • lightheadedness
  • headache
  • dry mouth, and
  • diarrhea as your body adjusts to the medication

Other side effects of Demser include:

  • depression
  • hallucinations
  • disorientation
  • confusion
  • stomach upset
  • vomiting, and
  • stomach pain

The recommended initial dosage of Demser for adults and children 12 years of age and older is 250 mg orally four times daily. This may be increased by 250 mg to 500 mg every day to a maximum of 4.0 g/day in divided doses. Demser may interact with chlorpromazine, fluphenazine, haloperidol, mesoridazine, perphenazine, thioridazine, or trifluoperazine. Tell your doctor all medications and supplements you use. During pregnancy, Demser should be used only when prescribed. It is unknown if this drug passes into breast milk. Consult your doctor before breastfeeding.

Our Demser (metyrosine) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is Patient Information in Detail?

Easy-to-read and understand detailed drug information and pill images for the patient or caregiver from Cerner Multum.

Demser in Detail - Patient Information: Side Effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

  • drooling;
  • difficulty speaking;
  • tremors;
  • muscle spasms;
  • disorientation;
  • diarrhea; or
  • painful urination.

Less serious side effects may include:

  • headache;
  • drowsiness;
  • depression, hallucinations, disorientation, and confusion;
  • stomach upset, vomiting, stomach pain; or
  • dry mouth.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Demser (Metyrosine)

What is Patient Information Overview?

A concise overview of the drug for the patient or caregiver from First DataBank.

Demser Overview - Patient Information: Side Effects

SIDE EFFECTS: Drowsiness, tiredness, dizziness, lightheadedness, dry mouth, and diarrhea may occur as your body adjusts to the medication. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

To lower your risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: difficulty speaking, drooling, unwanted/uncontrolled movements, muscle stiffness, shaking (tremor), decrease in sexual ability, tenderness/swelling of the breast.

Tell your doctor immediately if any of these rare but very serious side effects occur: mental/mood changes (e.g., confusion, depression, severe anxiety), painful urination, pink/bloody urine, change in the amount of urine.

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire patient information overview for Demser (Metyrosine)

What is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Demser FDA Prescribing Information: Side Effects
(Adverse Reactions)


Central Nervous System

Sedation: The most common adverse reaction to DEMSER (metyrosine) is moderate to severe sedation, which has been observed in almost all patients. It occurs at both low and high dosages. Sedative effects begin within the first 24 hours of therapy, are maximal after two to three days, and tend to wane during the next few days. Sedation usually is not obvious after one week unless the dosage is increased, but at dosages greater than 2000 mg/day some degree of sedation or fatigue may persist.

In most patients who experience sedation, temporary changes in sleep pattern occur following withdrawal of the drug. Changes consist of insomnia that may last for two or three days and feelings of increased alertness and ambition. Even patients who do not experience sedation while on DEMSER (metyrosine) may report symptoms of psychic stimulation when the drug is discontinued.

Extrapyramidal Signs: Extrapyramidal signs such as drooling, speech difficulty, and tremor have been reported in approximately 10 percent of patients. These occasionally have been accompanied by trismus and frank parkinsonism.

Anxiety and Psychic Disturbances: Anxiety and psychic disturbances such as depression, hallucinations, disorientation, and confusion may occur. These effects seem to be dose-dependent and may disappear with reduction of dosage.


Diarrhea occurs in about 10 percent of patients and may be severe. Anti-diarrheal agents may be required if continuation of DEMSER (metyrosine) is necessary.


Infrequently, slight swelling of the breast, galactorrhea, nasal stuffiness, decreased salivation, dry mouth, headache, nausea, vomiting, abdominal pain, and impotence or failure of ejaculation may occur. Crystalluria (see PRECAUTIONS) and transient dysuria and hematuria have been observed in a few patients. Hematologic disorders (including eosinophilia, anemia, thrombocytopenia, and thrombocytosis), increased SGOT levels, peripheral edema, and hypersensitivity reactions such as urticaria and pharyngeal edema have been reported rarely.

Read the entire FDA prescribing information for Demser (Metyrosine)

Demser - User Reviews

Demser User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Demser sorted by most helpful. Patient Discussions FAQs

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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