Clonidine and Guanfacine Uses, Side Effects, and Safety Recommendations

The Bottom Line

Clonidine and guanfacine began as treatments for hypertension but have been found useful in managing attention-deficit/hyperactivity disorder (ADHD). Both drugs can cause adverse effects such as drowsiness, headache, dry mouth, and slowed heart rate, which can be intensified after an overdose. Swallowing even one tablet or coming in contact with a patch can cause toxicity in a child.

The Full Story

If someone you know has high blood pressure or lives with a child diagnosed with attention-deficit/hyperactivity disorder (ADHD), you might have run across clonidine or guanfacine. These medications act at sites called alpha-2 receptors on brain cells to send a message to the body to relax blood vessels in the heart, kidneys, and other areas, which lowers blood pressure and heart rate. These drugs also seem to improve symptoms like hyperactivity, impulsive behavior, and distractibility in ADHD.

How Are Clonidine and Guanfacine Used?

Clonidine (1974) and guanfacine (1986) have been around for a long time. Both drugs started out as treatments for high blood pressure (hypertension or HTN). Over time, their use for HTN has declined, mainly because newer medications with greater effectiveness and fewer side effects have come along. Clonidine and guanfacine can both cause marked drowsiness and dizziness, which puts older adults at particular risk for falls. They also cause troublesome side effects such as lowered heart rate, dry mouth, and constipation. Both drugs are still prescribed occasionally for HTN, but usually only after several other types of medication have been tried.

Clonidine and guanfacine are also FDA-approved to treat ADHD in children aged 6 years and older. They can be used as the only medication or in combination with a stimulant like methylphenidiate (Ritalin) or amphetamine and dextroamphetamine (Adderall). Clonidine and guanfacine are not usually first-line treatment for ADHD because of their side effects. Drowsiness and dizziness can pose problems for school-age children as well as adults with ADHD. Both drugs also slow the pulse and lower blood pressure. However, their side effects are sometimes useful. When clonidine or guanfacine is added to a stimulant medication for ADHD, they not only add therapeutic benefit but can counteract some of the stimulant's side effects such as nervousness and tics.

Clonidine and guanfacine are available in different dosage forms for different purposes. Both come in short-acting (immediate-release or IR) tablets for HTN treatment, and long-acting (12- or 24-hour extended-release or ER) tablets to treat the symptoms of ADHD. In addition, clonidine is available as a weekly patch to treat HTN. The table below helps sort out the available products.






IR tablets: generic


Twice daily


Extended-release (ER) tablets: Kapvay or generic


Twice daily


Transdermal patch: Catapres TTS or generic


Change patch every 7 days


IR tablets: generic


Once daily


Extended-release (ER) tablets: Intuniv or generic


Once daily

What Should You Know About Taking Clonidine or Guanfacine?

Sedation and drowsiness occur in up to 60% of people taking these medications. Headache, dizziness, dry mouth, constipation, and erectile dysfunction might also occur, which sometimes cause patients to think about discontinuing their medication. Slowed heart rate can lead to complications in patients with heart disease. Finally, the drugs cannot be stopped abruptly because withdrawal is possible, causing blood pressure and heart rate to rise rapidly. Discontinuation is done by slow reductions in dosage over time.

Fortunately, there are many recommended alternatives to clonidine and guanfacine to treat HTN. In addition, patients who need clonidine for blood pressure control often find that using the transdermal patch, instead of pills, results in fewer and milder side effects.

Children and adults diagnosed with ADHD might be prescribed clonidine or guanfacine as a way to avoid using or in addition to stimulants like Ritalin and Adderall. The ER clonidine and guanfacine products that are used in ADHD treatment are absorbed gradually, so their side effects are generally milder than with IR products. In many cases, the adverse effects of clonidine and guanfacine lessen over time with continued use.

How Do Poisonings Happen?

If someone takes too much clonidine or guanfacine, they might develop adverse effects such as rapid onset of sedation, depression of breathing, low heart rate, and a drop in blood pressure. Hazardous side effects can occur even after an unintentional double-dose. Children who are prescribed one of the medications, or who unintentionally get into mom's purse or a grandparent's pill minder, tend to be even more sensitive to the side effects than adults.

These drugs are normally broken down in the liver, but many medications can interfere with this process to either intensify or reduce their beneficial or adverse effects. Be sure to ask your pharmacist whether any of your (or your child's) medications might interact with these drugs.

How Are Clonidine and Guanfacine Poisonings Treated?

Since even a small extra dose of clonidine or guanfacine might cause some risky side effects, Poison Control should be consulted to help you decide whether the amount taken was safe enough to watch at home or if a trip to an ER is needed. Poison Control will take into account information such as the person's age, weight, other health conditions, and the amount of medication that was possibly involved. In the case of extended-release tablets or a patch, drugs are released slowly and symptoms might not show up for many hours, so observation in an ER is often advised.

Clonidine patches present a special kind of toxic hazard, and any child exposed to a clonidine patch is likely to be referred an ER. Children who have swallowed, chewed on, or unintentionally applied clonidine patches to themselves have experienced unconsciousness, lapses in breathing, low blood pressure, and slowed heart rate. A child might obtain a used patch from a family member or even from the trash. It can take several hours before enough of the drug is released from the patch to cause symptoms, and by then the situation could be an emergency. Don't be fooled by thinking that a discarded patch doesn't contain much medication – a used clonidine patch can contain up to 75% of the original drug content. To safely dispose of a clonidine patch, fold the patch in half with the adhesive facing inward, and discard it in a trash can whose contents are safe from children and pets (e.g., can with a lid, outside trash).

Interestingly, the opiate antagonist naloxone (Narcan or Evzio) is sometime useful for treating toxicity with these drugs. Many of the symptoms of clonidine or guanfacine toxicity resemble those seen in an opioid overdose. Naloxone is not always effective with these drugs, but it is often tried before resorting to stronger measures to control breathing, blood pressure, and heart rate. For more information on opioids, see the June 2018 edition of the Poison Post®.

If you have questions about an adverse reaction or possible overdose of clonidine or guanfacine, immediately check the webPOISONCONTROL® online tool or call Poison Control at 1-800-222-1222 for help 24 hours a day, every day.

Leslie A. McCament-Mann, PhD, RPh
Clinical Toxicologist

For More Information

American Academy of Pediatrics, Subcommittee on Children and Adolescents with Attention-Deficit/Hyperactivity Disorder. Clinical practice guideline for the diagnosis, evaluation, and treatment of attention‚Äźdeficit/hyperactivity disorder in children and adolescents. Pediatrics Oct; 2019;144(4):1-26.

Attention-deficit/hyperactivity disorder (ADHD) Treatment Recommendations [Internet]. Atlanta: Centers for Disease Control and Prevention; 30 Sep 2019 [cited 18 Nov 2019].

High Blood Pressure [Internet]. Atlanta: Centers for Disease Control and Prevention; 2 Oct 2019 [cited 18 Nov 2019].2019.


Borys DJ, Blair HW, Morrissey RP, Morgan DL. Clinical effects and clinical outcomes following the ingestion of extended release guanfacine (Intuniv®) in children [abstract]. Clin Toxicol (Phila). 2011;49(6):551.

Caravati EM, Bennett DL. Clonidine transdermal patch poisoning. Ann Emerg Med. 1988 Feb;17(2):175-6.

Clonidine management. In: POISINDEX System (Micromedex 2.0). Greenwood Village CO: Truven Health Analytics; c2019 [cited12 Nov 2019].

Corneli HM, Banner WW, Vernon DD, Swenson PH. Toddler eats clonidine patch and nearly quits smoking for life. JAMA. 1989 Jan 6;261(1):42.

Fiser DH, Moss MM, Walker W. Critical care for clonidine poisoning in toddlers. Crit Care Med. 1990 Oct;18(10):1124-8.

Guanfacine management. In: POISINDEX System (Micromedex 2.0). Greenwood Village CO: Truven Health Analytics; c2019 [cited12 Nov 2019].

Klein-Schwartz W. Trends and toxic effects from pediatric clonidine exposures. Arch Pediatr Adolesc Med. 2002 Apr;156(4):392-6.

Lo JC, Vo T, Cortez-Gomez B, Cantrell L. A retrospective review of supratherapeutic ADHD medication ingestions in pediatric patients [abstract]. Clin Toxicol. 2012;50(7):606-7.

Reed MT, Hamburg EL. Person-to-person transfer of transdermal drug-delivery systems: a case report [Letter]. N Engl J Med. 1986 Apr 24;314(17):1120-1.

Spiller HA, Klein-Schwartz W, Colvin JM, Villalobos D, Johnson PB, Anderson DL. Toxic clonidine ingestion in children. J Pediatr. 2005 Feb;146(2):263-6.

Winograd EJ, Sollee D, Schauben JL, Kunisaki T, Smotherman C, Gautam S. Pediatric guanfacine exposures reported to the National Poison Data System, 2000-2016. Clin Toxicol (Phila). 2019 Apr 22:1-7. [Epub ahead of print]


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Prevention Tips

  • To avoid withdrawal symptoms, don't stop taking these medications abruptly.
  • Don't chew or crush extended-release tablets or capsules.
  • Unless directed by the prescriber, do not cut a clonidine patch in half.
  • Keep careful track of clonidine patches. If a patch is missing, locate it as soon as possible and make sure that no one has been exposed. Dispose of used clonidine patches in the trash carefully.
  • Ask your pharmacist about potential drug interactions between your other medications and clonidine or guanfacine. Include all prescription, over-the-counter, and herbal medications you take.
  • Keep all medicines – prescription and over-the-counter – securely out of the sight and reach of children and pets.

This Really Happened

Case 1. A clonidine patch had been worn for 5 days by an adult and was then discarded. A 9-month-old boy was later found sucking on the patch. He quickly became pale and lethargic, and his systolic blood pressure dropped to 38 mm Hg [normal is 80-100]. He required continuous intravenous medication for 6 hours to restore his blood pressure. The boy recovered fully in 24 hours (From Caravati et al., 1988).

Case 2. A 9-month-old boy was noted to be irritable and unusually drowsy after sleeping with his parents overnight. He was also extremely thirsty. The father, who had high blood pressure, discovered on arising in the morning that the clonidine patch he'd applied to his upper arm was missing. The boy's symptoms were at first blamed on a recent cold and teething. However, during the evening bath, the patch was discovered on the boy's back. Within 6 hours of patch removal, the boy's symptoms improved, and he was back to normal by the next morning (From Reed & Hamburg, 1986).

Case 3. A 3-year-old boy was thought to be napping, but somehow obtained a bottle containing 7 or 8 clonidine 0.1 mg immediate-release tablets. All of the tablets were missing. The child quickly became very drowsy. Poison Control immediately referred the child to the nearest hospital. The ER staff administered naloxone 2 mg and transferred him to the intensive care unit. He was very lethargic, and his breathing rate would drop when he was asleep. His heart rate was low at 60-65 beats per minute [normal for his age would be 90-150]. His blood pressure was also low. His symptoms were persistent but improving within 24 hours after the initial discovery of the ingestion. He went home the next day.

Case 4. A 4-year-old boy took his older sibling's guanfacine extended-release 1 mg tablet. This medication is not recommended for children under 6 years of age because depression of breathing and loss of consciousness can happen with as little as 1 mg. Symptoms can be delayed up to 8 hours due to the ER formulation and last for 24 hours or more. Poison Control referred the child to an emergency room. He was observed for 8 hours in the ER and fortunately remained asymptomatic.