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12 Hour Decongestant Side Effects

Generic name: pseudoephedrine

Medically reviewed by Last updated on Oct 25, 2023.

Note: This document contains side effect information about pseudoephedrine. Some dosage forms listed on this page may not apply to the brand name 12 Hour Decongestant.

Applies to pseudoephedrine: oral capsule liquid filled, oral liquid, oral solution, oral syrup, oral tablet, oral tablet extended release.

Serious side effects

Along with its needed effects, pseudoephedrine (the active ingredient contained in 12 Hour Decongestant) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur while taking pseudoephedrine:


- more common with high doses

Symptoms of overdose

Other side effects

Some side effects of pseudoephedrine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Less common

For Healthcare Professionals

Applies to pseudoephedrine: compounding powder, oral capsule, oral liquid, oral suspension extended release, oral tablet, oral tablet chewable, oral tablet extended release.


The most commonly reported adverse effects have included cardiovascular and (e.g. elevated blood pressure, tachycardia, or arrhythmias), CNS stimulation (e.g. restlessness, insomnia, anxiety, tremors, and rarely hallucinations), skin rashes, and urinary retention.[Ref]


Frequency not reported: Tachycardia, palpitations, arrhythmia, hypertension, impaired circulation to the extremities[Ref]

Nervous system

Frequency not reported: Headache, tremor


Frequency not reported: Dry mouth, nausea, vomiting


Frequency not reported: Hypersensitivity reactions including cross-sensitivity with other sympathomimetic[Ref]


Rare (less than 0.1%): Hallucinations

Frequency not reported: Restlessness, insomnia, sleep disturbances, anxiety, excitability[Ref]


Frequency not reported: Urinary retention, especially in men with prostatic enlargement


Frequency not reported: Angle-closure glaucoma


Frequency not reported: Skin rashes, fixed drug eruption in the form of erythematous nodular patches[Ref]


Post marketing reports: False-positive amphetamine immunoassay[Ref]

False-positives can occur far below the published threshold indicating that cross-reactivity in human specimens is sometimes greater than the limits reported.[Ref]

Frequently asked questions

More about 12 Hour Decongestant (pseudoephedrine)

Patient resources

Other brands

Sudafed Congestion, Sudafed 12-Hour, SudoGest, Sudafed 24-Hour, ... +14 more

Professional resources

Other brands


Related treatment guides


1. (2001) "Product Information. Sudafed (pseudoephedrine)." Glaxo Wellcome

2. Cerner Multum, Inc. "UK Summary of Product Characteristics."

3. Cerner Multum, Inc. "Australian Product Information."

4. Depriest AZ, Knight JL, Doering PL, Black DL (2012) "Pseudoephedrine and false-positive immunoassay urine drug tests for amphetamine." Pharmacotherapy

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.