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Brand & Generic Names


Basic Information

  • Habit forming? No
  • Prescription needed? Yes
  • Available as generic? Yes
  • Drug class: Antihypertensive


  • Treatment of high blood pressure and congestive heart failure.
  • Treatment of dysmenorrhea and menopausal "hot flashes."
  • Treatment of narcotic withdrawal syndrome.
  • Prevention of vascular headaches.

Dosage & Usage Information

How to take:
Tablet--Swallow with liquid.
Patches that attach to skin--Apply to clean, dry, hairless skin on arm or trunk.

When to take:
Daily dose at bedtime.

If you forget a dose:
Bedtime dose--If you forget your once-a- day dose, take it as soon as you remember. Don't double dose.

What drug does:
Relaxes and allows expansion of blood vessel walls.

Time lapse before drug works:
1 to 3 hours.

Don't take with:
Non-prescription medicines containing alcohol.
Any other medicine without consulting your doctor or pharmacist.


Vomiting, fainting, slow heartbeat, coma, diminished reflexes, shortness of breath, dizziness, extreme tiredness.


  • Dial 911 (emergency) or O (operator) for an ambulance or medical help. Then give first aid immediately.
  • If patient is unconscious and not breathing, give mouth-to- mouth breathing. If there is no heartbeat, use cardiac massage and mouth-to-mouth breathing (CPR). Don't try to make patient vomit. If you can't get help quickly, take patient to nearest emergency facility.
  • See EMERGENCY Information.

Possible Adverse Reactions or Side Effects


    In case of overdose, see Overdose section.


  • Dizziness, weight gain, drowsiness, lightheadedness upon rising from sitting or lying, swollen breasts.
  • Dry mouth, tiredness.


  • Abnormal heart rhythm.
  • Headache; painful glands in neck; nightmares; nausea; vomiting; cold fingers and toes; dry, burning eyes; depression.
  • Insomnia, constipation, appetite loss, diminished sex drive, nervousness.


    Rash, itch.

Warnings & Precautions

Don't take if:

  • You are allergic to any alpha-adrenergic blocker.
  • You are under age 12.

Before you start, consult your doctor:

  • If you will have surgery within 2 months, including dental surgery, requiring general or spinal anesthesia.
  • If you have heart disease or chronic kidney disease.
  • If you have a peripheral circulation disorder (intermittent claudication, Buerger's disease).
  • If you have history of depression.

Over age 60:
Adverse reactions and side effects may be more frequent and severe than in younger persons.

Studies inconclusive on harm to unborn child. Animal studies show fetal abnormalities. Decide with your doctor whether drug benefits justify risk to unborn child.

Unknown whether safe or not. Consult doctor.

Infants & children:
Use only under careful medical supervision after age 12. Avoid before age 12.

Prolonged use:

  • Don't discontinue without consulting doctor. Dose may require gradual reduction if you have taken drug for a long time. Doses of other drugs may also require adjustment.
  • Continued use may cause fluid retention, requiring addition of diuretic to treatment program.
  • Request yearly eye examinations.
  • Talk to your doctor about the need for follow-up medical examinations or laboratory studies.

Skin & sunlight:
No problems expected.

Driving, piloting or hazardous work:
Don't drive or pilot aircraft until you learn how medicine affects you. Don't work around dangerous machinery. Don't climb ladders or work in high places. Danger increases if you drink alcohol or take medicine affecting alertness and reflexes.

Don't discontinue abruptly. May cause rebound high blood pressure, anxiety, chest pain, insomnia, headache, nausea, irregular heartbeat, flushed face, sweating.

No problems expected.

Possible Interaction with Other Drugs

------------------------ -----------------------
ACE inhibitors*: Possible excessive
captopril, enalapril, potassium in blood.
Antidepressants, Decreased clonidine
tricyclic (TCA)* effect.
Antihypertensives, Excessive blood
other* pressure drop.
Appetite Decreased clonidine
suppressants* effect.
Beta-adrenergic Possible precipitous
blockers* change in blood pressure.
Carteolol Increased antihypertensive
Clozapine Toxic effect on the central nervous
Diuretics* Excessive blood pressure drop.
Ethinamate Dangerous increased effects of
ethinamate. Avoid combining.
Fenfluramine Possible increased clonidine
Fluoxetine Increased depressant effects of
both drugs.
Guanfacine Blood pressure control impaired.
Leucovorin High alcohol content of leucovorin
may cause adverse effects.
Methyprylon Increased sedative effect, perhaps
to dangerous level. Avoid.
Nabilone Greater depression of central
nervous system.
Nicardipine Blood pressure drop. Dosages may
require adjustment.
Nimodipine Dangerous blood pressure drop.
Nitrates* Possible excessive blood pressure
Sertraline Increased depressive effect of both
Sotalol Increased antihypertensive effect.
Terazosin Decreases effectiveness of

Possible Interaction with Other Substances

--------------- ---------------
Alcohol: Increased sensitivity to sedative
effect of alcohol and very low
blood pressure. Avoid.
Caffeine-containing Decreased clonidine
drinks. effect.
Cocaine Increased risk of heart block and
high blood pressure.
Foods: No problems expected.
Marijuana: Weakness on standing.
Tobacco: No problems expected.

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