G-Vent Side Effects
Generic Name: guaifenesin / phenylpropanolamine
Note: This page contains information about the side effects of guaifenesin / phenylpropanolamine. Some of the dosage forms included on this document may not apply to the brand name G-Vent.
Applies to guaifenesin / phenylpropanolamine: oral capsule extended release, oral liquid, oral tablet, oral tablet extended release
Cardiovascular adverse effects may be associated with the use of phenylpropanolamine. Phenylpropanolamine can cause a significant rise in heart rate. Hypertension and arrhythmias may be problematic in susceptible patients. Cardiovascular side effects have also included an increased risk of hemorrhagic stroke.[Ref]
Phenylpropanolamine causes vasoconstriction which usually does not result in blood pressure elevations in healthy adults given normally prescribed dosages. However, phenylpropanolamine administration may be problematic for patients with preexisting hypertension and those receiving higher dosages. In general, 75-mg of sustained-release phenylpropanolamine will not produce a significant increase in blood pressure in normotensive patients, but 150-mg of sustained-release phenylpropanolamine can.
The combination of caffeine and phenylpropanolamine is more apt to cause hypertension. Although caffeine is no longer added to phenylpropanolamine as an anorexiant, this combination is available as "look-alikes" for amphetamines. Hypertensive crisis has occurred occasionally subsequent to overuse, overdose, and ingestion of normally recommended doses. Hypertensive crisis may be accompanied by headache, blurred vision, confusion, intracranial hemorrhage, encephalopathy, or seizures.
Arrhythmias may be produced in predisposed patients. The majority of reports of arrhythmias involve overuse or overdose. Rarely, high doses of phenylpropanolamine may cause chest pain and evidence of myocardial injury.
One study reported that taking phenylpropanolamine increases the risk of hemorrhagic stroke in women. Men may also be at risk. Although the risk of hemorrhagic stoke is very low, the FDA recommends that all use of phenylpropanolamine be discontinued.[Ref]
Phenylpropanolamine produces nervous system stimulation, resulting in tremor, anxiety, insomnia, dizziness, and nervousness. Headache may also occur. Guaifenesin may rarely cause dizziness and headache.[Ref]
Seizures may occur in rare cases of hypertensive crisis due to phenylpropanolamine and have been reported with normally recommended doses as well as in cases of overuse or overdose.
There have been anecdotal reports of cerebrovascular hemorrhage largely associated with an uneven pattern of cerebrovascular spasm referred to as vascular beading. Vascular beading has also been reported in the absence of hemorrhage. Intracranial hemorrhage has almost always been associated with hypertension.[Ref]
Psychotic reactions to phenylpropanolamine have occurred in patients receiving normally recommended doses and in cases of abuse. In a few patients phenylpropanolamine appears to have exacerbated an underlying bipolar disorder which was previously undiagnosed.
A psychotic episode consisting of abnormal behavior was reported in a young woman following a week of therapy with Naldecon (phenylephrine, phenylpropanolamine, chlorpheniramine, and phenyltoloxamine) and amantadine. The patient had no personal or family history of psychiatric illness and no history of recreational substance use. It is uncertain whether the episode was due to the amantadine, the phenylpropanolamine or another component in the Naldecon, or an interaction between the drugs.[Ref]
Psychiatric reactions to phenylpropanolamine occur infrequently but include acute mania, anxiety, paranoia, confusion, agitation, and hallucinations. These reactions may be more common in women.[Ref]
Gastrointestinal complaints most commonly reported with phenylpropanolamine are anorexia and gastric irritation. Nausea and vomiting have occurred in conjunction with hypertensive episodes. Guaifenesin may cause gastrointestinal upset and vomiting, most often with higher than recommended doses.[Ref]
Hypersensitivity reactions to phenylpropanolamine may occur.[Ref]
Rarely, phenylpropanolamine may cause acute interstitial nephritis.[Ref]
Rash may rarely occur in patients taking guaifenesin.[Ref]
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Not all side effects for G-Vent may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.
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