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Side Effects


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 Demser (metyrosine) Side Effects Center for a complete guide to possible side effects


Caution should be observed in administering DEMSER (metyrosine) to patients receiving phenothiazines or haloperidol because the extrapyramidal effects of these drugs can be expected to be potentiated by inhibition of catecholamine synthesis.

Concurrent use of DEMSER (metyrosine) with alcohol or other CNS depressants can increase their sedative effects. (See WARNINGS and PRECAUTIONS: Information for Patients.)

Laboratory Test Interference

Spurious increases in urinary catecholamines may be observed in patients receiving DEMSER (metyrosine) due to the presence of metabolites of the drug.

Read the Demser Drug Interactions Center for a complete guide to possible interactions

This monograph has been modified to include the generic and brand name in many instances.

Last reviewed on RxList: 11/20/2008

Side Effects

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