Skip to Content

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.

As well as its needed effects, phenoxybenzamine may cause unwanted side effects that require medical attention.

Minor Side Effects

Some phenoxybenzamine side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned 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.

It is possible that some side effects of phenoxybenzamine may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.