Guanfacine (Intuniv): how it works, what it does and the risks

What guanfacine (Intuniv) is and how it's thought to work

Guanfacine is a non-stimulant ADHD medicine, sold in Australia as Intuniv and as generic guanfacine modified-release tablets in 1 mg to 4 mg strengths. Modified-release means the tablet releases the medicine slowly, so it is taken once a day.

Guanfacine began as a blood pressure medicine, and the Australian product information still calls it "a known antihypertensive agent". It is a selective alpha-2A adrenergic receptor agonist: it switches on one type of noradrenaline receptor. Preclinical research suggests that acting on these receptors in the prefrontal cortex (the front of the brain, involved in attention, planning and impulse control) changes noradrenaline signalling in a way that supports attention and reduces impulsiveness. The same action on the nerves to the heart and blood vessels is why lower blood pressure and a slower heart rate turn up as side effects.

It is not a stimulant. Stimulants work for the hours a dose is active; guanfacine builds up slowly and has, in the product information's words, "no known potential for abuse or dependence". For the other options, see our ADHD medication guide.

What the evidence shows

Children and teenagers

• Placebo-controlled trials. In an 8-week trial of 6 to 17 year olds, Biederman and colleagues (2008) found 2 mg, 3 mg and 4 mg daily doses all reduced ADHD rating scale scores more than placebo.
• A European trial with an atomoxetine arm. Hervas and colleagues (2014) randomised 338 children and teenagers to guanfacine, atomoxetine or placebo for 10 to 13 weeks. Guanfacine cut scores 8.9 points more than placebo (effect size 0.76); 67.9% were rated much or very much improved against 44.1% on placebo. Atomoxetine was a reference arm, not a head-to-head test, and the PBS advisory committee later called the superiority claim questionable.
• Meta-analyses. Hirota and colleagues (2014) pooled 12 trials of alpha-2 agonists (guanfacine and clonidine) in 2,276 young people: a medium-sized effect alone (standardised mean difference 0.59), smaller when added to a stimulant (0.36).

How it compares with stimulants

The 2018 Lancet Psychiatry network meta-analysis (Cortese and colleagues, 133 trials) found every medicine studied, guanfacine included, beat placebo in children at about 12 weeks, with the largest effects for amphetamines and methylphenidate; more children stopped guanfacine than placebo because of side effects. Australian Prescriber's 2025 review states that non-stimulants are less effective than stimulants, and the Australian ADHD guideline (AADPA, 2022) recommends a stimulant first, offering atomoxetine, guanfacine or clonidine when stimulants are contraindicated, not tolerated, ineffective at adequate doses, or useful as an add-on.

Tics and Tourette syndrome

Guanfacine is often raised when a child has tics, because stimulants can make tics worse, and Healthdirect lists Tourette syndrome as a reason to try a non-stimulant. Scahill and colleagues (2001) randomised 34 children aged 7 to 14 with a tic disorder plus ADHD to immediate-release guanfacine (not the Intuniv tablet) or placebo for 8 weeks: teacher-rated ADHD scores fell 37% against 8%, and tic severity fell 31% against no change. One trial of 34 children makes it an option worth discussing, not a proven treatment for tics.

Adults

One placebo-controlled adult trial, from Japan, is the basis of guanfacine's adult approval there. Iwanami and colleagues (2020) randomised 201 adults to guanfacine (2 to 6 mg) or placebo for 12 weeks. Scores fell 11.6 points against 7.3 on placebo (effect size 0.52), but 19.8% stopped because of side effects against 3.0%. In a 2025 review of 113 adult trials (Ostinelli and colleagues), stimulants and atomoxetine were the medicines with clear benefit over placebo, and more adults stopped guanfacine than placebo. The AADPA guideline still lists guanfacine as a second-line option for adults, which in Australia means off-label prescribing.

Side effects and risks

Common side effects

In the pooled trials of guanfacine alone (1,419 children and teenagers), the product information lists sleepiness, headache, tiredness and stomach pain as very common (more than 1 in 10), and sedation, dizziness, slow heart rate, low blood pressure, nausea, reduced appetite, weight gain and irritability as common. In the European trial, 43.9% of children on guanfacine reported sleepiness, 26.3% headache and 25.4% tiredness; across seven trials, sleepiness was about five times as likely as on placebo.

Blood pressure, heart rate and fainting

The product information reports dose-dependent falls of 6 to 9 beats per minute in heart rate and 4 to 5 mmHg in systolic blood pressure, and warns that guanfacine "can cause syncope, hypotension, and bradycardia" (fainting, low blood pressure and slow heart rate). A 2025 analysis of 102 trials (Farhat and colleagues) found the same, with larger falls in adults, and advised monitoring blood pressure and pulse on any ADHD medicine.

Weight, growth and mood

Because weight and BMI can rise, height, weight and BMI are checked before starting, every 3 months in the first year and 6-monthly after that. The product information notes post-marketing reports of suicide-related events with ADHD medicines as a group, and the consumer medicine information asks you to tell the doctor about any history of suicidal thoughts.

Sedation, driving, alcohol and interactions

The product information says not to drive or operate machinery if you feel dizzy, sleepy or tired on it, and to avoid alcohol; other sedating medicines add to the effect. Guanfacine is broken down by the liver enzyme CYP3A4: the antifungal ketoconazole roughly tripled exposure, and the antibiotic rifampicin cut it by about 70%. Other listed interactions are blood-pressure-lowering medicines, valproate, sedatives, benzodiazepines and antipsychotics, and grapefruit juice and high-fat meals.

Overdose

Overdose can cause low blood pressure, slow heart rate, drowsiness and slowed breathing. A child who becomes lethargic after taking too much should be observed for up to 24 hours, because coma, slow heart rate and low blood pressure can develop late. The Poisons Information Centre is 13 11 26.

Who shouldn't take it, and who needs extra care

The only contraindication is known hypersensitivity (allergy) to guanfacine or the tablet's ingredients. Caution is advised with a history of low blood pressure, heart block, slow heart rate, other heart disease or fainting, and the consumer information asks you to tell the doctor about liver or kidney problems and any history of suicidal thoughts. In pregnancy it is Category B3, used only if the potential benefit outweighs the potential risk to the baby; it isn't known whether it passes into breast milk, so caution is advised when breastfeeding.

Questions to ask the prescriber

• Why guanfacine rather than a stimulant, atomoxetine or clonidine, and is it being added to a stimulant or replacing one?
• What dose will we build up to, over how many weeks, and when should we expect to see a difference?
• How often will blood pressure, heart rate, weight and height be checked, and what are the warning signs of low blood pressure or fainting?
• What should we do about a missed dose, and what is the plan if we want to stop?
• Does it interact with any other medicines, including antibiotics, antifungals or epilepsy medicines?

This guide is general information, not medical advice. Decisions about starting, changing or stopping guanfacine are made with the prescribing doctor.