Hyperreactive individuals may display ephedrine-like reactions such as tachycardia, palpitations, headache, dizziness, or nausea. Sympathomimetic amines have been associated with certain untoward reactions including fear, anxiety, nervousness, restlessness, tremor, weakness, pallor, respiratory difficulty, dysuria, insomnia, hallucinations, convulsions, CNS depression, arrhythmias, and cardiovascular collapse with hypotension.

Guaifenesin is well tolerated and has a wide margin of safety. Side effects are generally mild and infrequent. Nausea and vomiting are the most frequently occurring side effects.

Drug Abuse And Dependence

Central nervous system stimulants have been abused. At high doses, subjects commonly experience an elevation of mood, a sense of increased energy and alertness, and decreased appetite. Some individuals become anxious, irritable and loquacious. In addition to the marked euphoria, the user experiences a sense of markedly enhanced physical strength and mental capacity. With continued use, tolerance develops, the user increases the dose, and toxic signs and symptoms appear. Depression may follow rapid withdrawal.

Read the Pseudovent 400 Capsules (pseudoephedrine hcl extended-release and guaifenesin) Side Effects Center for a complete guide to possible side effects »

Beta-adrenergic blockers and MAO inhibitors may potentiate the pressor effect of pseudoephedrine. Concurrent use of digitalis glycosides may increase the possibility of cardiac arrhythmias. Sympathomimetics may reduce the hypotensive effects of guanethidine, mecamylamine, methyldopa, reserpine and veratrum alkaloids. Concurrent use of tricyclic antidepressants may antagonize the effects of pseudoephedrine. Use of other vasopressor drugs during halothane anesthesia may cause serious cardiac arrhythmias.

Drug/Laboratory Test Interactions

Guaifenesin interferes with the colorimetric determination of 5-hydroxyindoleacetic acid (5-HIAA) and vanilylmandelic acid (VMA). Administration of the drug should be discontinued 48 hours prior to the collection of urine specimens for such tests.

Last reviewed on RxList: 3/24/2008
This monograph has been modified to include the generic and brand name in many instances.