Clonidine: what it treats, how to take it, side effects
Last updated September 3, 2026.
Clonidine is a centrally acting alpha agonist - it slows your heart rate and relaxes blood vessels from the brain's control center outward. You may know it as Catapres. It treats high blood pressure, and in extended-release form it treats ADHD in children - and it has the strictest do-not-stop-suddenly rule in its class.
What does it treat?
High blood pressure, alone or combined with other medications, and - as the extended-release tablet or suspension - ADHD in children 6 and older, as part of a full treatment program that may include counseling and special education. MedlinePlus also lists uses for painful menstrual cramps, menopausal hot flashes, hypertensive crisis, alcohol and opiate withdrawal, and smoking cessation.
How do you take it?
With or without food, same times every day. The regular tablet is usually twice a day at evenly spaced intervals; the extended-release forms go once a day (once or twice for ADHD), with the oral suspension at bedtime. Swallow extended-release tablets whole - never split, chew, or crush - and shake the suspension 10 seconds before measuring with the supplied syringe. Your doctor starts low and increases no more than once a week. The rule above all rules: never stop suddenly. MedlinePlus warns that sudden stopping causes a rapid blood pressure rise with fast heartbeat, nervousness, anxiety, headache, nausea, flushing, lightheadedness, chest tightness, and uncontrollable shaking - every exit is a gradual taper over days. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: dry mouth, tiredness, weakness, headache, nervousness, decreased sexual ability, nausea, vomiting, and constipation. Drowsiness and dizziness are common enough that driving waits until you know your response, and standing up fast can bring fainting - rise slowly, and drink plenty of fluids and stay cool, because dehydration and overheating raise the fainting risk.
- Serious - call your doctor immediately or get emergency care: rash, hives, swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs, and difficulty swallowing or breathing.
Who should not take it?
Flag stroke, a heart attack or any heart rhythm problem, high or low blood pressure, kidney disease, fainting history, and any past skin reaction to clonidine patches. Alcohol makes the side effects worse - ask your doctor for the rule. If you become pregnant, call your doctor. And a storage warning with teeth: the label reports that as little as 0.1 mg of clonidine has produced toxicity in children, with overdose signs within 30 minutes to 2 hours - keep every tablet locked away and out of sight.
When is it an emergency?
Trouble breathing or swallowing, or facial or throat swelling, is a 911 call. A child swallowing any clonidine is an immediate emergency - do not wait for symptoms. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why is clonidine so dangerous to stop suddenly?
Rebound. MedlinePlus warns that suddenly stopping clonidine can cause a rapid rise in blood pressure, with fast heartbeat, nervousness, anxiety, headache, nausea, flushing, lightheadedness, chest tightness, and uncontrollable shaking. The brain recalibrates around the drug, and yanking it away lets pressure surge. Every stop is a gradual taper over days, directed by your doctor.
Why is clonidine prescribed for ADHD when it is a blood pressure drug?
Different target, same calming effect. MedlinePlus explains the extended-release form treats ADHD in children 6 and older by affecting the part of the brain that controls attention and impulsivity - and it works as part of a full program that may include counseling and special education, not as a solo fix. The blood pressure drug and the ADHD drug are different formulations on different schedules.
Why does clonidine make my mouth so dry?
It turns down the same nerve signals everywhere, not just in your blood vessels. Dry mouth tops MedlinePlus's common-effects list for this drug. Water, sugar-free gum or candy, and saliva substitutes are the standard counters; if it becomes unbearable, your doctor can adjust the dose or the drug.
Can I drink alcohol while taking clonidine?
Ask your doctor - MedlinePlus says alcohol can make clonidine's side effects worse, and the effects it worsens are the drowsiness, dizziness, and fainting risk. The explicit personal rule comes from your prescriber.
Why do I faint more easily in the heat on clonidine?
Pressure control plus dehydration. MedlinePlus warns you may faint if you become dehydrated or overheated on this medication - clonidine lowers pressure, and heat and fluid loss lower it further. Drink plenty of liquids, stay cool in hot weather, and rise slowly from lying down, especially in the first weeks.
What happens if a child swallows a clonidine tablet?
Treat it as an emergency immediately. The label reports that as little as 0.1 mg has produced toxicity in children, with overdose signs appearing within 30 minutes to 2 hours - drowsiness, slow heart rate, breathing problems. Do not wait for symptoms: call Poison Control at 1-800-222-1222 or go to the emergency room, and store every tablet locked and out of sight.