Phenylephrine, sold under the brand names Neosynephrine and Sudafed PE among others, is a medication used as a decongestant for uncomplicated nasal congestion in the form of a nasal spray or oral tablet,[5] to dilate the pupil, to increase blood pressure given intravenously in cases of low blood pressure, and to relieve hemorrhoids as a suppository.
[12] Severe side effects may include a slow heart rate, intestinal ischemia, chest pain, kidney failure, and tissue death at the site of injection.
[23] In November 2024, the FDA proposed to remove oral phenylephrine as an active ingredient that can be used in over-the-counter (OTC) monograph drug products for the temporary relief of nasal congestion.
[24] Phenylephrine is used as an alternative to pseudoephedrine as a decongestant, whose availability has been restricted in some countries due to a potential for use in the illicit synthesis of methamphetamine.
[25] Its efficacy as an oral decongestant has been questioned, with several independent studies finding that it provided no more relief to sinus congestion than a placebo.
[12] Two studies published in 2009, examined the effects of phenylephrine on symptoms of allergic rhinitis by exposing people to pollen in a controlled, indoor environment.
Since 2004, phenylephrine has been increasingly marketed as a substitute for pseudoephedrine; some manufacturers have changed the active ingredients of products to avoid restrictions on sales.
[citation needed] In September 2023, an independent advisory committee to the U.S. Food and Drug Administration (FDA) unanimously agreed that there is insufficient evidence showing that "orally administered phenylephrine is effective as a nasal decongestant".
[23][34] In November 2024, the FDA proposed to remove oral phenylephrine as an active ingredient that can be used in over-the-counter (OTC) monograph drug products for the temporary relief of nasal congestion.
Phenylephrine causes the constriction of vascular smooth muscle and is often used in the treatment of hemorrhoids to narrow the swollen veins and relieve the attendant pain.
Products for treatment may also include substances that will form a protective barrier over the inflamed area, resulting in less pain when feces are passed.
[38] Phenylephrine has been used as an intracameral injection into the anterior chamber of the eye to arrest intraocular bleeding occurring during cataract and glaucoma surgery.
[8] Additionally, an over-the-counter dose of 60 mg produces a slight increase in heart rate with no detectable changes in blood pressure.
[8] However, other literature reports that doses over 15 mg affect the cardiovascular system, including increases in blood pressure and decreases in heart rate.
[6][7] These other drugs include antihistamines like chlorpheniramine, doxylamine, promethazine, and mepyramine (pyrilamine); analgesics like paracetamol (acetaminophen), ibuprofen, ketorolac, and codeine; cough suppressants like dextromethorphan; expectorants like guiafenesin; anticholinergics like cyclopentolate and tropicamide; and β-adrenergic receptor agonists like isoprenaline (isoproterenol).
[6][7] It is used in combination with antihistamines and analgesics in cough and cold preparations, with anticholinergics in ophthalmic formulations, and with β-adrenergic receptor agonists in inhalational forms.
Because this medication is a sympathomimetic amine without β-adrenergic receptor agonist activity, it does not increase contractility force and output of the cardiac muscle.
It may increase blood pressure resulting in a slow heart rate through stimulation of vascular (likely carotid) baroreceptors.
[11] In people with underlying cardiovascular disease, phenylephrine has been found to increase blood pressure and cause associated impairment in myocardial perfusion.
[11] Other reported side effects of phenylephrine have included increased blood pressure, vasoconstriction resulting in worsened orthostatic tolerance, atrial fibrillation following coronary artery bypass surgery, decreased cerebral oxygenation, bradycardia in people with spinal cord injury, cardiac arrhythmias, pulmonary edema, myocardial infarction, and microvascular occlusion syndrome.
Some patients have been shown to have an upset stomach, severe abdominal cramping, and vomiting issues connected to taking this drug.
[5] In addition, combination of phenylephrine with other sympathomimetic drugs can increase pressor effects and the risk of hemorrhagic stroke.
[5] Other drugs that may decrease the effects of phenylephrine may include calcium channel blockers, ACE inhibitors and benzodiazepines.
[53] Patients taking these medications may need a higher dose of phenylephrine to achieve a comparable increase in blood pressure.
[11] Phenylephrine is a selective agonist of the α1-adrenergic receptor, one of the biological targets of the catecholamine hormones and neurotransmitters epinephrine (adrenaline) and norepinephrine (noradrenaline).
[55] Because of its α1-adrenergic receptor agonism, phenylephrine is a directly acting sympathomimetic vasoconstrictor[8][15] and produces both venous and arterial vasoconstriction.
[8][46] The lack of central permeation with phenylephrine is in contrast to certain other related decongestant and sympathomimetic agents like pseudoephedrine, ephedrine, and phenylpropanolamine.
[3][9] Unlike phenylephrine, related sympathomimetics with a methyl group at the α carbon (i.e., amphetamines), like ephedrine, pseudoephedrine, phenylpropanolamine, methoxamine, and methoxyphenamine, are resistant to degradation by monoamine oxidase.
[1][57][3] It is closely structurally related to epinephrine (adrenaline; 3,4,β-trihydroxy-N-methylphenethylamine), differing from it only in the absence of one hydroxyl group on the phenyl ring.
[1][2][61][4] Synonyms of phenylephrine include phenephrine, fenefrine, L-m-synephrine, metaoxedrine, neo-oxedrine, mesatonum, neosynephrine, and m-sympatol.