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Phenoxybenzamine Side Effects

For the Consumer

Applies to phenoxybenzamine: oral capsule

In rats and mice, phenoxybenzamine has been found to increase the risk of development of malignant tumors. It is not known if phenoxybenzamine increases the chance of tumors in humans.

Along with its needed effects, phenoxybenzamine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Some side effects of phenoxybenzamine 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
  • Dizziness or lightheadedness, especially when getting up from a lying or sitting position
  • fast heartbeat
  • pinpoint pupils
  • stuffy nose
Less common
  • Confusion
  • drowsiness
  • dryness of mouth
  • headache
  • lack of energy
  • sexual problems in males
  • unusual tiredness or weakness

For Healthcare Professionals

Applies to phenoxybenzamine: compounding powder, oral capsule


Cardiovascular side effects have included postural hypotension and tachycardia. These symptoms are evidence of adrenergic blockade and vary according to the degree of blockade.[Ref]


Genitourinary side effects have included inhibition of ejaculation. This symptom is indicative of adrenergic blockade and varies according to the degree of blockade.[Ref]


Respiratory side effects have included nasal congestion. This symptom is indicative of adrenergic blockade and varies according to the degree of blockade.[Ref]


Ocular side effects have included miosis. This symptom is indicative of adrenergic blockade and varies according to the degree of blockade.[Ref]

Nervous system

Nervous system side effects have included drowsiness and fatigue.[Ref]


Gastrointestinal side effects have included gastrointestinal irritation.[Ref]


1. "Product Information. Dibenzyline Capsules (phenoxybenzamine)." SmithKline Beecham, Philadelphia, PA.

Some side effects of phenoxybenzamine may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

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