Guanfacine: what it treats, how to take it, side effects
Last updated September 3, 2026.
Guanfacine is a non-stimulant that does double duty: high blood pressure in one form, ADHD in another. You may know it as Tenex (the blood pressure tablet) or Intuniv (the extended-release ADHD tablet). It is a centrally acting alpha2A-adrenergic agonist that decreases heart rate and relaxes blood vessels, and it is one of the few ADHD options that is not a stimulant and not a controlled substance.
What does it treat?
Two different jobs. The immediate-release tablet (Tenex) treats high blood pressure, alone or combined with other medications. The extended-release tablet (Intuniv) controls ADHD symptoms in children, as part of a treatment program, by affecting the part of the brain that controls attention and impulsivity. Never take both products - they are the same active ingredient.
How do you take it?
Once a day, same time every day. The immediate-release tablet is usually taken at bedtime; the extended-release tablet is taken once daily and must not be taken with a high-fat meal, which changes absorption. Swallow extended-release tablets whole with water - never break, chew, or crush them. Your doctor starts low and increases gradually - no more than once a week for the extended-release, every 3 to 4 weeks for the tablet. Full benefit takes about 2 weeks. Do not stop suddenly: blood pressure can rebound up and you may become nervous or anxious, so your doctor decreases the dose gradually. 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, irritability, decreased sexual ability, decreased appetite, stomach pain, nausea, vomiting, and constipation.
- Serious: fainting, blurred vision, rash, and slow heart rate - call your doctor immediately for these. Drowsiness and dizziness are expected, especially early: no driving until you know how it affects you.
Who should not take it?
Anyone already taking the other guanfacine product - Tenex and Intuniv together is double-dosing the same drug. Tell your doctor if you have ever fainted, and about a recent heart attack, stroke, low blood pressure, slow heart rate, bipolar disorder, and heart, kidney, or liver disease. St. John's wort and OTC allergy medications (diphenhydramine, loratadine, fexofenadine, chlorpheniramine, cetirizine) interact - flag them before starting. Tell the surgeon or dentist before any procedure. Alcohol can make its side effects worse, so ask your doctor about it. Pregnancy and breastfeeding need a direct call.
When is it an emergency?
Fainting is the big one - call your doctor immediately, and 911 if someone cannot be awakened or has trouble breathing. For an overdose (drowsiness, lack of energy, slow heart rate, fainting), 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
What is the difference between Tenex and Intuniv?
Same drug, different jobs and release. Tenex is the immediate-release tablet, usually taken at bedtime for high blood pressure. Intuniv is the extended-release tablet taken once daily for ADHD in children. MedlinePlus warns never to take both at the same time - they are the same active ingredient, so that is a double dose.
Is guanfacine a stimulant like Adderall?
No - and that is its appeal for some families. Guanfacine is a centrally acting alpha2A-adrenergic agonist: not a stimulant, not a controlled substance, no habit-forming warning. It calms the part of the brain that controls attention and impulsivity rather than speeding it up, and it gets used alone or alongside a stimulant.
Why can't Intuniv be taken with a high-fat meal?
Fat changes absorption. MedlinePlus says the extended-release tablet should not be taken with a high-fat meal - the fat pushes more drug into the bloodstream faster than intended, spiking side effects like sleepiness and low blood pressure. A normal breakfast is fine; a fast-food breakfast sandwich is not.
Why can't I stop guanfacine suddenly?
Rebound. MedlinePlus says if you suddenly stop taking guanfacine, your blood pressure may increase and you may become nervous or anxious - your doctor will decrease the dose gradually. This is a blood pressure drug at its core, and blood pressure drugs punish sudden stops.
Can I drink alcohol while taking guanfacine?
Ask your doctor first. MedlinePlus says alcohol can make the side effects of guanfacine worse - and the side effects in question are drowsiness, dizziness, and low blood pressure, which alcohol multiplies. Light or none is the realistic guidance.
How long does guanfacine take to work for ADHD?
MedlinePlus says it may take 2 weeks before you feel the full benefit of the extended-release tablets, with dose increases no more than once a week. Early sleepiness is the most common reason families worry in week one - it typically fades as the body adjusts.