Phenylpropalamine: Formula, Indications, Mechanism of Action, Dosage, Side Effects, Warnings, Contraindications and Interactions

It is a stimulant drug of the central nervous system, which is a substance with vasoconstrictor properties.

Phenylpropanolamine, also called phenylpropanolamine, has been used in obesity treatments and is one of the ingredients used in flu and decongestant medications.

On November 6, 2000, the Food and Drug Administration asked all pharmaceutical companies to discontinue phenylpropanolamine marketing products.

This is a public health advisory advising consumers against the use of over-the-counter medications such as cold and allergy medicine or weight control products that contain phenylpropanolamine hydrochloride.

In the final report on hemorrhagic stroke studies, the Yale University School of Medicine noted that phenylpropanolamine increased the risk of hemorrhagic strokes in women. Men may also be at risk of developing them.

The potential for abuse and adverse effects have limited routine use as a decongestant and appetite suppressant in human medicine.

Most human preparations have been phased out of the market, and the only readily available forms are those marketed for veterinary medicine.


The chemical formula of phenylpropanolamine

  • C9H13NO.


Oral formulations of phenylpropanolamine for veterinary use are available in capsule or syrup form.

Indications of phenylpropanolamine

Phenylpropanolamine has been used as a decongestant, as a mild bronchodilator, and to increase urinary sphincter tone.

Pseudoephedrine and ephedrine are related drugs that produce similar alpha and beta receptor effects.

The most common use in animals today is to treat urinary incontinence. The mechanism for this action appears to be through stimulant receptors in the sphincter.

It has also been used to treat dogs’ priapism (persistent erection).

Mechanism of action

Phenylpropanolamine directly stimulates alpha-adrenergic receptors and produces vasoconstriction; it also reduces tissue hyperemia, edema, and nasal congestion.

Phenylpropanolamine indirectly stimulates beta receptors, producing tachycardia and a positive inotropic effect.

Dose of phenylpropanolamine

The dose used in dogs is as follows:

  1. A dose of 1 mg per kilogram of the dog’s weight every 8 hours.
  2. A dose of 1 to 1.5 mg per kilogram of the dog’s weight every 12 hours.

Toxic dose

Phenylpropanolamine is toxic in doses greater than 1.5 mg per kilogram of body weight and causes vomiting, tachycardia, hyperactivity, hyperthermia, and hypertension.

Side effects

Phenylpropanolamine has been found to increase the risk of hemorrhagic stroke (bleeding in the brain or the tissue surrounding the brain) in women, and men may also be at risk.

Although the risk of hemorrhagic stroke is shallow, it has been recommended not to use in humans.

Several studies have reported aggression, anorexia, cardiac arrhythmia, hypertension, and diarrhea due to the use of phenylpropanolamine in animals.

Sympathomimetics can produce a wide range of effects, most of which mimic the results of excessive stimulation of the sympathetic nervous system.

Phenylpropanolamine overdose would likely produce symptoms of excessive stimulation of the sympathetic nervous system.

Signs of aggression and restlessness have been observed in some dogs using treatment.

Likewise, dogs’ lethargy and loss of appetite have been reported after an overdose.

Warnings and Contraindications

Phenylpropanolamine is not a selective α-adrenergic receptor agonist; although it shows some residual potency in β-adrenoceptors, its use is contraindicated in pregnant and lactating animals.

Clinical signs of phenylpropanolamine poisoning include hyperactivity, hyperthermia, mydriasis, tachyarrhythmias or bradycardia, hypertension, agitation, and seizures.

This medicine should not be used in patients with severe hypertension, ventricular tachycardia, or in patients who are hypersensitive to phenylpropanolamine or any of the components of the formula.

Phenylpropanolamine interactions

When used in combination with β-adrenergic receptor blockers, especially non-selective β-adrenergic blockers, phenylpropanolamine can cause a sharp increase in peripheral vascular resistance.

During anesthesia with inhalational narcotics such as halothane and isoflurane, phenylpropanolamine can induce cardiac arrhythmia and, therefore, should not be used only under medical caution or surveillance.