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Clonidine: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on July 13, 2023.

1. How it works

  • Clonidine may be used to treat high blood pressure and some other conditions such as attention deficit hyperactivity disorder (ADHD).
  • Clonidine acts on specific receptors in the brain stem called alpha-adrenoreceptors to reduce heart rate and blood pressure.
  • The mode of action of clonidine in ADHD is not known.
  • Clonidine belongs to the class of drugs known as centrally-acting alpha agonists.

2. Upsides

  • Clonidine may be used in the treatment of high blood pressure after other treatments have failed. It is usually used in combination with other agents for high blood pressure.
  • Slow-release forms (Kapvay brand) may be used in the treatment of ADHD (Attention Deficit Hyperactivity Disorder) in children over the age of six years.
  • May also be used off-label for other conditions, such as Tourette's syndrome (off-label means not an FDA-approved use but experts consider it still has a place in therapy).
  • Available as an oral tablet, a transdermal patch, and an oral extended-release tablet. The incidence of side effects may be lower with the transdermal patch compared with oral forms of the drug but people using this patch should be monitored for the appearance of a rash.
  • Generic clonidine is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Dry mouth, drowsiness, headache, fatigue, dizziness on standing, dry eyes, and constipation. Clonidine may lower blood pressure and increase the risk of falls when going from a lying or sitting position to standing. Drowsiness caused by clonidine may affect a person's ability to drive or operate machinery.
  • Other less common effects include agitation, anxiety, hallucinations, skin reactions, slow heart rate, and increased sensitivity to alcohol. A skin rash associated with clonidine use has been reported.
  • May cause a withdrawal reaction with abrupt discontinuation (symptoms include anxiety, agitation, tremor, and headache accompanied by a rapid rise in blood pressure); taper off slowly on a doctor's advice and reinstate clonidine if necessary.
  • Transdermal clonidine may be associated with an initially localized skin rash at the site of application; continued use may see a more generalized rash develop - seek immediate medical advice.
  • Clonidine may worsen or cause arrhythmias, especially when used with other medications that affect the sympathetic nervous system (such as epinephrine).
  • May not be suitable for some people including those with previous allergic reactions to clonidine.
  • Be cautious when using for children, especially those with a gastrointestinal illness that may cause vomiting and inadequate tablet absorption.
  • May be administered up until 4 hours before surgery and then reinstated soon after.
  • A dosage reduction may be necessary for elderly people.
  • Clonidine should only be used during pregnancy if the benefits outweigh the risks. Clonidine is excreted into breast milk so caution should be exercised when administering it to a lactating woman.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Clonidine can be used to lower blood pressure and treat ADHD; however, it causes sedation, and tolerance can develop to its blood pressure-lowering effects. Clonidine should not be stopped suddenly but withdrawn slowly over a few days.

5. Tips

  • Avoid driving or operating machinery until the effects of clonidine on your functioning are known.
  • Formulations of clonidine are not interchangeable; speak to your pharmacist.
  • Do not crush or chew slow-release forms of clonidine; swallow whole.
  • Food does not affect the absorption of clonidine.
  • Do not stop taking it without your doctor's advice; slow withdrawal over at least 2 to 4 days may be necessary.
  • Regular monitoring of blood pressure and kidney function may be needed.
  • Dry eyes caused by clonidine may affect contact lens wear; try lubricant eye drops or seek medical advice.
  • Taking most of your designated dose of clonidine at night may help reduce the incidence of daytime sedation and dry mouth.
  • If you miss a dose, take the next dose as scheduled; do not take more than the prescribed amount in a daily period.

6. Response and effectiveness

  • Clonidine is rapidly absorbed and the peak effects are seen within one to three hours. The blood pressure-lowering effect of clonidine happens quickly, within 30 to 60 minutes after an oral dose, and the maximal effect on blood pressure occurs within two to four hours.
  • May be used in addition to other medications for ADHD. An improvement in the symptoms of ADHD attributable to clonidine may take several days to develop.

7. Interactions

Medicines that interact with clonidine may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with clonidine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with clonidine include:

  • alpha-blockers such as prazosin or terazosin
  • amphetamines which may diminish the blood pressure-lowering effects of clonidine
  • antidepressants, such as fluoxetine, paroxetine, St John’s Wort, monoamine oxidase inhibitors, and tricyclic antidepressants (such as amitriptyline, imipramine, and nortriptyline)
  • beta-blockers such as atenolol or metoprolol
  • calcium channel blockers, such as diltiazem or verapamil
  • cyclosporine
  • digoxin
  • duloxetine
  • levodopa
  • methylphenidate
  • opioids, such as oxycodone or morphine
  • some medications used to treat mental illness, such as clozapine or thioridazine
  • zolpidem.

Clonidine may interact with other medications that affect the heart rate.

Note that this list is not all-inclusive and includes only common medications that may interact with clonidine. You should refer to the prescribing information for clonidine for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use clonidine only for the indication prescribed.

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

Copyright 1996-2023 Revision date: July 13, 2023.