Guanfacine

What it is

Guanfacine is a synthetic small-molecule drug that selectively stimulates alpha-2A adrenergic receptors in the brain and the sympathetic nervous system. It was first marketed as an immediate-release tablet for high blood pressure, and a separate extended-release tablet was later approved for attention-deficit/hyperactivity disorder in children and adolescents. The two formulations are not interchangeable on a mg-per-mg basis because their blood-level profiles differ. It is not a stimulant and is cleared mainly by the liver enzyme CYP3A4 and by the kidney.

What the research says

For ADHD, the evidence is reasonably strong but modest in size: pooled randomised trials put the extended-release drug's effect on ADHD symptoms at about half a standard deviation, smaller than methylphenidate or amphetamines, and in the largest network meta-analysis guanfacine did not beat placebo on teacher-rated symptoms and was less well tolerated than placebo in children. For high blood pressure, the immediate-release drug lowers blood pressure about as well as clonidine in trials from the 1980s, but there are no modern cardiovascular outcome trials. For tics, a placebo-controlled trial was negative. For PTSD, two placebo-controlled trials in veterans were negative. The main harms are sedation, low blood pressure, slow heart rate and fainting, and blood pressure can rebound above baseline if the drug is stopped abruptly.

Evidence grade: Well established.

How it works

Drug class: Selective alpha-2A adrenergic receptor agonist (centrally acting sympatholytic / non-stimulant ADHD medicine)

Guanfacine switches on alpha-2A adrenergic receptors. In the brainstem vasomotor centre this damps down sympathetic nerve traffic to the heart and blood vessels, which lowers blood pressure and heart rate. In the prefrontal cortex the same receptors are thought to strengthen signalling involved in attention and impulse control, which is the proposed basis for its effect in ADHD. (Source 1)

What it is used for

• Multiple placebo-controlled trials and a meta-analysis of alpha-2 agonist trials show a real but moderate reduction in ADHD symptoms (pooled SMD about -0.59 as monotherapy, about -0.36 as add-on). The largest network meta-analysis ranked it below methylphenidate and amphetamines and found it less well tolerated than placebo in this age group. Evidence: established. (Source 2)
• One phase 3 placebo-controlled trial in Japanese adults found a between-group effect size of 0.52 on the ADHD rating scale, but about one in five participants stopped because of side effects versus 3% on placebo. The approved indication differs by country. Evidence: limited. (Source 3)
• Blood-pressure-lowering is well documented - in a 24-week randomised comparison 55% of guanfacine-treated patients reached a diastolic target, similar to clonidine. We found no randomised trial of guanfacine reporting heart attack, stroke or death as an outcome, so the benefit is established for the surrogate (blood pressure) and not for hard events. Evidence: limited. (Source 4)
• An 8-week randomised placebo-controlled trial in 34 children found tics improved about equally in both arms (effect size 0.35 on guanfacine versus 0.38 on placebo) and the authors concluded the results did not justify a larger efficacy trial. Evidence: not-supported. (Source 5)
• A pilot randomised trial (62 on drug, 21 on placebo) was designed for safety, not efficacy. It found no difference between groups on the two anxiety rating scales, with a higher clinician-rated global improvement rate on drug (54.2% versus 31.6%) that was not tested statistically. Evidence: limited. (Source 6)
• Two randomised placebo-controlled trials in veterans with chronic PTSD found no benefit on clinician-rated or self-reported symptoms, sleep or mood. Evidence: not-supported. (Source 7)
• A 2024 scoping review found only case reports and retrospective cohorts - no controlled trials - and no reduction in intensive care or hospital length of stay. Evidence: unknown. (Source 8)

Interactions

• Strong and moderate CYP3A4 inhibitors (for example ketoconazole, fluconazole, clarithromycin, ritonavir) (pharmacokinetic study): These drugs block the liver enzyme that breaks guanfacine down, so guanfacine levels rise and sedation, low blood pressure and slow heart rate become more likely. The label tells prescribers to halve the target dose. (Source 9)
• Strong and moderate CYP3A4 inducers (for example rifampin, carbamazepine, efavirenz) (pharmacokinetic study): These speed up guanfacine's breakdown, so levels fall and the drug may stop working. The label tells prescribers to consider doubling the target dose. (Source 9)
• St John's wort (Hypericum perforatum) (theoretical): St John's wort is a well-known inducer of CYP3A4, the enzyme that clears guanfacine, so it would be expected to lower guanfacine levels and reduce its effect. We found no study that measured this for guanfacine specifically, so this is an inference from the drug's metabolism, not a measured interaction. (Source 9)
• Grapefruit and grapefruit juice (theoretical): Grapefruit inhibits intestinal CYP3A4 and would be expected to raise guanfacine levels. No grapefruit-guanfacine study exists that we could find, so this is inferred from the pathway rather than measured. (Source 9)
• A high-fat meal (pharmacokinetic study): Taking the extended-release tablet with a high-fat breakfast raised peak blood levels by about 75% and total exposure by about 40% compared with taking it on an empty stomach. The label says not to take it with high-fat meals. (Source 10)
• Alcohol (label): Alcohol and guanfacine both depress the central nervous system, so sleepiness and dizziness can add together. The label advises avoiding alcohol while taking it. (Source 11)
• Other blood-pressure-lowering drugs and anything that slows the heart (label): Effects on blood pressure and heart rate add together, raising the chance of dizziness and fainting. The label asks for blood pressure and heart rate monitoring and dose adjustment. (Source 12)

Stopping it

• Abrupt stopping has produced rebound hypertension above the starting level, with reported hypertensive encephalopathy; the risk looks higher on high doses and with a stimulant also on board, and children who vomit and cannot take a dose are specifically flagged. (Source 13)
• Even with a planned taper, average blood pressure and heart rate in five paediatric trials ended up slightly above where they started, and in one maintenance study it took an estimated six to twelve months to return to baseline. (Source 14)
• The label's taper is a decrement of no more than 1 mg every 3 to 7 days, with blood pressure and pulse checked while coming off. (Source 13)
• In adults with hypertension, blind substitution of placebo for long-term guanfacine let blood pressure drift back up over two to four days rather than spiking, and no one showed symptoms of catecholamine excess within 48 hours - a slower offset than clonidine. (Source 15)
• In a head-to-head withdrawal comparison, stopping clonidine abruptly produced a rapid blood pressure rise whereas stopping guanfacine produced a more gradual one, with a significant difference over the first three days. (Source 4)

What goes wrong

Sedation, fatigue and somnolence are common on alpha-2 agonists, with numbers needed to harm as low as 4 for somnolence. (Source 2)

• Meta-analysis, Moderate certainty.
• Size: 2,276 participants across 12 randomised trials.
• Who: children and adolescents with ADHD.
• How long: short-term trials.
• Result: fatigue NNH = 10, sedation NNH = 17, somnolence NNH = 4 for monotherapy; somnolence NNH = 10 when added to a stimulant; greater hypotensive, bradycardic and QTc-prolonging effects than placebo.
• Funding: not stated in the abstract.

significantly more common fatigue (NNH = 10), sedation (NNH = 17), and somnolence (NNH = 4)

Guanfacine was less well tolerated than placebo in children and adolescents, measured as dropouts caused by side effects. (Source 16)

• Meta-analysis, Low certainty.
• Size: 11,018 children and adolescents in the tolerability analysis.
• Who: children and adolescents with ADHD.
• How long: timepoints closest to 12 weeks.
• Result: odds ratio for dropping out because of side effects 2.64 (95% CI 1.20-5.81) versus placebo, in children and adolescents only.
• Funding: Stichting Eunethydis and the UK NIHR (non-industry)

guanfacine was inferior to placebo in children and adolescents only

In the manufacturer's pooled paediatric trials, low blood pressure was reported more than twice as often on guanfacine as on placebo, and 1% of children fainted. (Source 17)

• Official position, Moderate certainty.
• Size: pooled short-term monotherapy trials plus the long-term open-label programme.
• Who: children and adolescents aged 6 to 17 taking guanfacine extended-release.
• How long: short-term controlled trials and open-label follow-up of about 10 months.
• Result: hypotension 7% on drug versus 3% on placebo; orthostatic hypotension 1% versus 0%; maximum mean falls of -5.4 mmHg systolic, -3.4 mmHg diastolic and -5.5 bpm pulse; syncope in 1% of paediatric patients.
• Funding: manufacturer document (regulatory label)

Hypotension was reported as an adverse reaction for 7% of the INTUNIV group and 3% of the placebo group.

Fainting has been reported in children taking guanfacine with no other identified cause. (Source 18)

• Case series, Very low certainty.
• Size: 4 children.
• Who: children with Tourette's syndrome treated with guanfacine.
• How long: not stated.
• Result: 4 syncopal episodes attributed to drug-induced hypotension or bradycardia.
• Funding: not stated.

We report on 4 children who experienced a syncopal episode while being treated with guanfacine without any other evident cause.

Guanfacine blood levels are associated with a small lengthening of the QT interval and a fall in heart rate. (Source 19)

• Blood level study, Low certainty.
• Size: population model built on the paediatric trial programme.
• Who: paediatric patients taking guanfacine extended-release.
• How long: model of pooled trial data.
• Result: about 1 ms QTcP increase per 1 ng/mL of guanfacine (slope 0.941 ms per ng/mL, 95% CI 0.62-1.25); heart rate fell about 2.3% of baseline per 1 ng/mL.
• Funding: manufacturer-affiliated analysis.

Guanfacine exposure was associated with small decreases in HR and a small prolongation of the population-corrected QT (QTcP) interval.

Stopping guanfacine abruptly has caused blood pressure to rebound above its starting level, and hypertensive encephalopathy has been reported. (Source 13)

• Official position, Low certainty.
• Size: post-marketing case reports.
• Who: children and adults who stopped guanfacine abruptly, often on high doses and often also taking a stimulant.
• How long: not applicable.
• Result: clinically significant and persistent rebound hypertension above baseline, increases in heart rate, and reported hypertensive encephalopathy.
• Funding: manufacturer document (regulatory label)

abrupt discontinuation of INTUNIV has resulted in clinically significant and persistent rebound hypertension above baseline levels and increases in heart rate

What the evidence supports

Alpha-2 agonists including guanfacine reduce ADHD symptoms in children more than placebo, with a moderate effect size as monotherapy and a smaller one when added to a stimulant. (Source 2)

• Meta-analysis, Moderate certainty.
• Size: 2,276 participants across 12 randomised trials (9 monotherapy trials, n = 1,550; 3 add-on trials, n = 726)
• Who: children and adolescents with ADHD.
• How long: short-term trials (mostly 6 to 13 weeks)
• Result: monotherapy SMD -0.59 (p < .00001) for overall ADHD symptoms; add-on SMD -0.36 (p < .0001); all-cause discontinuation RR 0.70, NNT = 10.
• Funding: not stated in the abstract; the underlying trials were largely manufacturer-sponsored.

agonist monotherapy significantly reduced overall ADHD symptoms (SMD = -0.59, p < .00001)

In the pivotal fixed-dose trial, guanfacine extended-release reduced ADHD rating scale scores at every dose from 1 mg to 4 mg. (Source 20)

• Randomized trial, Moderate certainty.
• Size: 345 children and adolescents aged 6 to 17 randomised across four doses and placebo.
• Who: 6- to 17-year-olds meeting ADHD criteria.
• How long: 9 weeks.
• Result: effect sizes 0.43 to 0.62 on the ADHD Rating Scale-IV total score; mean heart rate and blood pressure fell as dose rose.
• Funding: manufacturer-sponsored (Shire)

Statistically significant reductions in ADHD Rating Scale-IV scores were observed from baseline to endpoint at all doses of GXR, with effect sizes ranging from 0.43 to 0.62.

Immediate-release guanfacine lowered blood pressure about as effectively as clonidine, with less somnolence. (Source 4)

• Randomized trial, Low certainty.
• Size: 546 randomised (270 guanfacine, 276 clonidine)
• Who: adults with mild to moderate essential hypertension already on chlorthalidone.
• How long: 24 weeks.
• Result: 55% of guanfacine versus 59% of clonidine patients reached diastolic blood pressure 90 mmHg or less; somnolence 21% versus 35% (p < 0.05); dry mouth 30% versus 37%.
• Funding: not stated in the abstract; 1980s manufacturer-era comparative trial.

The 2 agents had equal efficacy; 149 of 270 patients treated with guanfacine (55%) and 164 of 276 treated with clonidine (59%) achieved goal diastolic BP of less than or equal to 90 mm Hg.

What the evidence does not support

In the largest network meta-analysis of ADHD drugs, guanfacine was not shown to beat placebo on teacher-rated symptoms, and the authors did not recommend it as a first-choice drug. (Source 16)

• Meta-analysis, Low certainty.
• Size: 133 double-blind randomised trials; 10,068 children and adolescents in the 12-week efficacy analysis.
• Who: children, adolescents and adults with ADHD.
• How long: timepoints closest to 12 weeks.
• Result: on teachers' ratings only methylphenidate (SMD -0.82, 95% CI -1.16 to -0.48) and modafinil (-0.76, -1.15 to -0.37) beat placebo; the review's confidence in estimates ranged from high or moderate to low or very low for most indirect comparisons.
• Funding: Stichting Eunethydis and the UK NIHR Oxford Health Biomedical Research Centre (non-industry)

for available comparisons based on teachers' ratings, only methylphenidate

Guanfacine extended-release did not reduce tic severity more than placebo in children with chronic tic disorders. (Source 5)

• Randomized trial, Low certainty.
• Size: 34 children (16 guanfacine, 18 placebo)
• Who: children aged 6 to 17 with chronic tic disorders including Tourette's disorder.
• How long: 8 weeks.
• Result: YGTSS total fell from 26.3 to 23.6 on guanfacine (p = 0.08, effect size 0.35) and from 27.7 to 24.7 on placebo (p = 0.08, effect size 0.38); CGI-I response 19% (3/16) versus 22% (4/18), p = 1.0.
• Funding: not stated in the abstract; investigator-initiated pilot study.

These results do not support the launch of a larger efficacy trial for tics in children and adolescents with CTD.

Guanfacine did not improve PTSD symptoms in veterans in a randomised placebo-controlled trial. (Source 7)

• Randomized trial, Low certainty.
• Size: 63 veterans (29 guanfacine, 34 placebo)
• Who: veterans with chronic PTSD, medication-free or on stable pharmacotherapy.
• How long: 8 weeks.
• Result: no effect on PTSD symptoms, subjective sleep quality or general mood disturbance; side effects were more common on drug.
• Funding: not stated in the abstract.

Guanfacine had no effect on PTSD symptoms, subjective sleep quality, or general mood disturbances.

A second randomised placebo-controlled trial of guanfacine in veterans with PTSD also found no difference from placebo. (Source 21)

• Randomized trial, Very low certainty.
• Size: small sample of predominantly male combat veterans (exact n not given in the abstract)
• Who: patients with chronic PTSD on stable antidepressants.
• How long: 8 weeks double-blind plus 2-month open label.
• Result: no significant differences on CAPS, MADRS, CGI-S, CGI-I or the Davidson Trauma Scale.
• Funding: not stated in the abstract.

There were no significant differences in the drug versus placebo responses for the clinician-administered or patient self-report outcome measures

In a pilot trial in children with anxiety disorders, guanfacine extended-release did not separate from placebo on the anxiety rating scales. (Source 6)

• Randomized trial, Very low certainty.
• Size: 83 randomised (62 guanfacine, 21 placebo)
• Who: children aged 6 to 17 with generalised, separation or social anxiety disorder.
• How long: 12 weeks.
• Result: no differences on the Pediatric Anxiety Rating Scale or SCARED; CGI-I 2 or better in 54.2% versus 31.6%, but no inferential statistics were performed.
• Funding: manufacturer supplied study drug; exploratory feasibility study.

No differences were observed between treatment groups for PARS and SCARED scores

Guanfacine for delirium in hospital has not been tested in any controlled trial and did not shorten intensive care or hospital stay in the available studies. (Source 8)

• Systematic review, Very low certainty.
• Size: 908 articles screened; 2 case reports, 1 case series, 3 retrospective cohorts included.
• Who: hospitalised patients with delirium.
• How long: median time to delirium improvement 3 days.
• Result: no association with decreased intensive care or hospital length of stay; most frequent adverse events mild hypotension and bradycardia.
• Funding: not stated in the abstract.

There is limited data on the efficacy of guanfacine for the treatment of delirium.

Where the evidence is mixed

In adolescents, guanfacine extended-release beat placebo on ADHD symptoms but did not improve either measured domain of day-to-day functioning. (Source 22)

• Randomized trial, Moderate certainty.
• Size: 314 randomised (157 drug, 157 placebo)
• Who: adolescents aged 13 to 17 with ADHD.
• How long: 13 weeks.
• Result: ADHD-RS-IV change -24.55 versus -18.53, effect size 0.52, p < .001; CGI-S improvement 50.6% versus 36.1%, p = .010; no significant difference in either Weiss Functional Impairment domain; 46.5% needed a dose above the then-approved 4 mg maximum.
• Funding: manufacturer-sponsored (Shire)

There was no statistically significant difference between treatments at week 13 in the 2 WFIRS-P domains.

Where the research disagrees

Whether guanfacine should be used as a first-choice ADHD medicine

• Cortese and colleagues, European ADHD Guidelines Group network meta-analysis (2018), network meta-analysis of 133 double-blind randomised trials, confidence in estimates high to very low: evidence from this meta-analysis supports methylphenidate in children and adolescents, and amphetamines in adults, as preferred first-choice medications for the short-term treatment of ADHD (Source 23)
• Hirota and colleagues, alpha-2 agonist meta-analysis (2014), meta-analysis of 12 randomised trials of alpha-2 agonists, N = 2,276: Agonist monotherapy and, possibly to a lesser extent, co-treatment, are significantly superior to placebo for overall, hyperactivity, and inattentive ADHD symptoms (Source 24)

Whether guanfacine helps tics

• Murphy and colleagues (2017), 8-week randomised double-blind placebo-controlled pilot trial, n = 34: These results do not support the launch of a larger efficacy trial for tics in children and adolescents with CTD (Source 5)
• Pringsheim and colleagues (2015), reviewing disruptive behaviour in ADHD, systematic review and meta-analysis with GRADE rating, 2 systematic reviews and 20 randomised trials; this addresses oppositional behaviour rather than tics: There is moderate-quality evidence that guanfacine has a small-to-moderate effect on oppositional behaviour in youth with ADHD, with and without ODD (Source 25)

How much

• Reference intake: There is no reference intake for a drug: the dose is chosen by the prescriber. As a position, the 2025 US Intuniv label states a weight-based target range of 0.05 to 0.12 mg/kg/day, equal to a total daily dose of 1 to 7 mg once daily. (Source 26)
• Upper limit: As a position, the 2025 US Intuniv label puts the top of the target range at 7 mg/day total, reached by increments of no more than 1 mg per week; this is the label's figure, not a safety threshold derived from toxicology. (Source 26)
• Studied: The pivotal paediatric trial randomised 6- to 17-year-olds to fixed once-daily doses of 1, 2, 3 or 4 mg or placebo for 9 weeks. (Source 20)
• Studied: The adult phase 3 trial titrated from 2 mg/day to 4-6 mg/day, then maintained 4-6 mg/day, then tapered back to 2 mg/day. (Source 3)
• Studied: The negative tic trial reached a mean final daily dose of 2.6 mg. (Source 5)
• Studied: The 1980s hypertension comparison used guanfacine as step-2 therapy added to 25 mg of chlorthalidone once a day. (Source 4)

A common belief, and what the research shows

The belief: Guanfacine is just an old blood pressure tablet, so it is a mild and harmless alternative to stimulants.

What the research shows: It lowers blood pressure and heart rate in everyone who takes it, and stopping it suddenly can push blood pressure above where it started. The label records that "abrupt discontinuation of INTUNIV has resulted in clinically significant and persistent rebound hypertension above baseline levels and increases in heart rate", with hypertensive encephalopathy also reported. In the pooled trials "Hypotension was reported as an adverse reaction for 7% of the INTUNIV group and 3% of the placebo group." and in the largest network meta-analysis "guanfacine was inferior to placebo in children and adolescents only" on dropouts caused by side effects.

Questions and answers

What is it?

Guanfacine is a prescription medicine that switches on alpha-2A adrenergic receptors in the brain and nervous system. It comes as an immediate-release tablet used for high blood pressure and as a separate extended-release tablet used for ADHD. The two are not interchangeable on a mg-per-mg basis. It is not a stimulant. (Source 1)

What does it do in the body?

By acting on alpha-2A receptors in the brainstem it reduces sympathetic nerve traffic to the heart and blood vessels, which lowers peripheral resistance, blood pressure and heart rate. The same receptors in the prefrontal cortex are the proposed route by which it improves attention and impulse control. Its ADHD effect in trials is moderate, roughly half a standard deviation. (Source 1)

Is it good or bad for you?

It depends on the use. For ADHD in children the evidence supports a moderate benefit, but the same pooled trials show sedation, fatigue, low blood pressure and slow heart rate occur often enough that one extra child in four becomes sleepy. For tics and PTSD, randomised trials were negative. For blood pressure it works on the number but has never been tested against heart attacks or strokes. (Source 24)

How do you get more of it?

Guanfacine is a prescription-only synthetic drug. There is no food or supplement source, and the amount a person takes is decided and adjusted by a prescriber. As a position, the 2025 US label describes a weight-based target range of 0.05 to 0.12 mg/kg/day, equal to 1 to 7 mg once daily, reached in steps of no more than 1 mg a week. (Source 26)

If it is harmful, what reduces it?

Reducing or stopping guanfacine is what lowers its effects, but this is the step with the clearest documented harm: abrupt stopping has caused rebound hypertension above baseline and hypertensive encephalopathy. The label's method is a slow taper with blood pressure and pulse monitoring rather than simply stopping. (Source 13)

Why might someone be low in it or missing it?

Being low on guanfacine is not a deficiency state - nobody needs it unless it has been prescribed. Blood levels can, however, be lower than intended if someone is also taking a CYP3A4 inducer such as rifampin or carbamazepine, or higher than intended on a CYP3A4 inhibitor or with a high-fat meal. Body weight is the main predictor of exposure in children. (Source 9)

Which whole foods contain it or feed it?

No whole food contains guanfacine. Food matters only because it changes absorption: a high-fat breakfast raised peak levels about 75% and total exposure about 40% compared with fasting, which is why the label says not to take the extended-release tablet with high-fat meals. (Source 10)

What happens if you do not have it?

Someone who has never taken it loses nothing. Someone who stops after taking it may see ADHD symptoms return, and will see blood pressure and heart rate rise - in five paediatric trials, even a tapered stop left mean blood pressure about 3 mmHg and heart rate about 5 bpm above the original baseline, taking an estimated six to twelve months to settle in one study. (Source 14)

How can you test for it?

There is no blood test used in practice to check a guanfacine level, and no diagnostic test for needing it. What is actually monitored is heart rate and blood pressure, before starting, after each dose increase, periodically on treatment and while coming off. Population pharmacokinetic models exist for research but are not clinical tests. (Source 12)

References

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2. Journal of the American Academy of Child and Adolescent Psychiatry. Alpha-2 agonists for attention-deficit/hyperactivity disorder in youth: a systematic review and meta-analysis of monotherapy and add-on trials to stimulant therapy. 2014. PMID 24472251, DOI 10.1016/j.jaac.2013.11.009. Read the source
3. The Journal of clinical psychiatry. Efficacy and Safety of Guanfacine Extended-Release in the Treatment of Attention-Deficit/Hyperactivity Disorder in Adults: Results of a Randomized, Double-Blind, Placebo-Controlled Study. 2020. PMID 32297719, DOI 10.4088/jcp.19m12979. Read the source
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23. The lancet. Psychiatry. Comparative efficacy and tolerability of medications for attention-deficit hyperactivity disorder in children, adolescents, and adults: a systematic review and network meta-analysis. 2018. PMID 30097390, DOI 10.1016/s2215-0366(18)30269-4. Read the source
24. Journal of the American Academy of Child and Adolescent Psychiatry. Alpha-2 agonists for attention-deficit/hyperactivity disorder in youth: a systematic review and meta-analysis of monotherapy and add-on trials to stimulant therapy. 2014. PMID 24472251, DOI 10.1016/j.jaac.2013.11.009. Read the source
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