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Hylorel Side Effects

Generic Name: guanadrel

Note: This document contains side effect information about guanadrel. Some of the dosage forms listed on this page may not apply to the brand name Hylorel.

For the Consumer

Applies to guanadrel: oral tablet

Along with its needed effects, guanadrel (the active ingredient contained in Hylorel) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Get emergency help immediately if any of the following symptoms of overdose occur while taking guanadrel:


  • Blurred vision
  • dizziness or faintness (severe)

Check with your doctor as soon as possible if any of the following side effects occur while taking guanadrel:

More Common

  • Swelling of feet or lower legs

Less Common or Rare

  • Chest pain
  • shortness of breath

Some side effects of guanadrel 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

  • Difficulty in ejaculating
  • dizziness, lightheadedness, or fainting, especially when getting up from a lying or sitting position
  • drowsiness
  • unusual tiredness or weakness
  • weight gain or loss (excessive)

Less Common or Rare

  • Diarrhea or increase in bowel movements
  • dryness of mouth
  • headache
  • muscle pain or tremors
  • nighttime urination

For Healthcare Professionals

Applies to guanadrel: oral tablet

Nervous system

The most common problems associated with guanadrel (the active ingredient contained in Hylorel) affect the nervous system. Up to 60% of patients have experienced drowsiness, fatigue, or headaches, 25% of patients experienced paresthesias or visual disturbances, and 2% experienced sleep disorders during therapy[Ref]


Cardiovascular side effects can result from excessive sympathetic blockade or a relative increase in parasympathetic tone. Orthostatic hypotension occurs in 8% to 50% of patients, some of whom experience syncope.

Unopposed or excessive parasympathetic tone can cause excessive bradycardia in rare cases. This may cause serious problems in patients with underlying sinus node dysfunction.

Peripheral edema has been reported in up to 30% of patients.

Other cardiovascular problems include chest pain in 28%, dyspnea at rest in 18%, dyspnea on exertion in 46%, and palpitations in 30% of patients. Underlying diseases may account for the relatively high incidence of some of these side effects.[Ref]

The risk of orthostatic hypotension, sometimes followed by syncope, is greatest within the first 10 minutes after dosing or early in the morning, and in hypovolemia. It is accentuated by alcohol, hot weather, or exercise--all of which are associated with peripheral vasodilation. The manufacturer recommends that guanadrel be gradually withdrawn over at least two weeks prior to administration of general anesthetics to avoid cardiovascular collapse during induction.[Ref]


Gastrointestinal side effects are also related to increased parasympathetic tone. Diarrhea has been reported in 5% to 30% of patients, some of whom discontinue therapy because of it. Constipation has been reported in up to 21% of patients. Dry mouth or parotid tenderness have been associated with the use of this drug in approximately 2% of patients.[Ref]


There is evidence that peripherally-acting antiadrenergic drugs may interfere with ejaculation by inhibiting contraction of the seminal vesicle, ampula and ductus deferens.[Ref]

Sexual impotence is a relatively common genitourinary complaint, occurring in 5% to 18% of male patients. Smaller studies, where specific questions were asked, revealed an incidence of impotence as high as 60% of male patients who were receiving a similar drug, guanethidine. Impotence appears to be reversible upon discontinuation of therapy or reduction in dosage. Urinary frequency or urgency has occurred in 30% to 50% of patients.[Ref]


Musculoskeletal cramping has occurred in approximately 20% to 40% of patients.[Ref]


1. Owens SD, Dunn MI "Efficacy and safety of guanadrel in elderly hypertensive patients." Arch Intern Med 148 (1988): 1515-8

2. Hansson L, Pascual A, Julius S "Comparison of guanadrel and guanethidine." Clin Pharmacol Ther 14 (1973): 204-8

3. Bloomfield DK, Cangiano JL "Guanadrel and guanethidine in hypertension." Clin Pharmacol Ther 11 (1970): 200-4

4. Gore RD "Safety and efficacy of a three-drug regimen for the treatment of hypertension: hydrochlorothiazide, propranolol, and guanadrel." Clin Ther 6 (1983): 86-93

5. Palmer JD, Nugent CA "Guanadrel sulfate: a postganglionic sympathetic inhibitor for the treatment of mild to moderate hypertension." Pharmacotherapy 3 (1983): 220-9

6. Dunn MI, Dunlap JL "Guanadrel. A new antihypertensive drug." JAMA 245 (1981): 1639-42

7. Finnerty FA, Jr Brogden RN "Guanadrel. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use in hypertension." Drugs 30 (1985): 22-31

8. Bloomfield DK, Cangiano JL "Clinical experience with a new antihypertensive agent, guanadrel sulfate." Curr Ther Res Clin Exp 11 (1969): 727-35

9. "Product Information. Hylorel (guanadrel)." Rhone-Poulenc Rorer, Collegeville, PA.

10. Rubenfeld S, Patten BM, Kohler PO "Effects of guanadrel on patients with thyrotoxicosis." Arch Intern Med 138 (1978): 1106-8

11. "Guanadrel (Hylorel)--a new antihypertensive drug." Med Lett Drugs Ther 25 (1983): 95-6

12. Hogikyan RV, Supiano MA "Homologous upregulation of human arterial alpha-adrenergic responses by guanadrel." J Clin Invest 91 (1993): 1429-35

13. Malinow SH "Comparison of guanadrel and guanethidine efficacy and side effects." Clin Ther 5 (1983): 284-9

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.