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Why Guanfacine Matters
Guanfacine is a repurposed antihypertensive with a real, if narrow, home in psychiatry. It is not a stimulant, it is not a controlled substance, and it does not touch striatal dopamine. That profile is exactly why it matters: in a field where the most effective ADHD drugs are Schedule II agents with abuse liability, guanfacine is a non-abusable, refillable alternative you can hand to patients you would hesitate to give a stimulant.
Be clear-eyed about it, though. As monotherapy for uncomplicated ADHD, guanfacine is a third-line drug: its effect size (~0.5) is meaningfully smaller than stimulants (0.8–0.9), it takes weeks to work, and it is not especially well tolerated, since sedation and dropout rates run higher than the psychiatric average. If a patient can safely take a stimulant and wants their ADHD treated well, a stimulant is the better drug.
It earns its keep in two places:
- ADHD complicated by a comorbidity that stimulants worsen: bipolar disorder, active or past substance use, tics, prominent anxiety or agitation, borderline personality disorder, sleep-onset problems. Here guanfacine's liabilities (sedation, modest efficacy) become tolerable trade-offs against a stimulant's liabilities (mania, misuse, tic exacerbation, insomnia).
- As an adjunct to a stimulant. This is arguably its best-evidenced role. Adding guanfacine to a stimulant beats either alone, and in one trial blood pressure rose less on the combination than on the stimulant alone (McCracken 2016). It does not reliably reduce guanfacine's own sedation.
The thesis of this guide: guanfacine is a tolerability-and-comorbidity play, not an efficacy play. Use it when the clinical situation rewards its specific profile (no abuse potential, calming rather than activating, benign in bipolar illness) and titrate it slowly while watching the heart rate and blood pressure. Prescribed that way, it is a useful drug. Prescribed as a first-line stimulant substitute for a straightforward ADHD patient, it will mostly disappoint.
Guanfacine is not a faster-acting or gentler stimulant: it is a different mechanism, and it works more slowly and less powerfully. Patients who expect a stimulant-like "switch flips on" experience will quit before it has a chance to work. Tell them: "This builds over two to five weeks, you won't feel a jolt, and we're choosing it because of your [tics / bipolar disorder / history with substances], not because it's the strongest ADHD drug."
Part 1: Indications
FDA-Approved
- ADHD in children and adolescents (ages 6–17), as the extended-release formulation (Intuniv), approved 2009–2010, both as monotherapy and as adjunct to stimulants.
- Hypertension (the immediate-release tablet, Tenex, is an older antihypertensive; this is guanfacine's original indication and is a non-psychiatric use).
Note that Intuniv is not FDA-approved for adult ADHD. Adult use rests on a single positive RCT (below) and is off-label.
The Evidence-Based Clinical Uses
Pediatric ADHD, the home indication. Two pivotal trials established efficacy vs. placebo. Read the subgroups carefully, though, because they shape who benefits:
- Biederman 2008 (Pediatrics, n=345, doses 2–4 mg): Intuniv beat placebo overall. On subgroup analysis, the signal was strongest in younger children (ages 6–8) and in combined-type ADHD; it was weaker or absent in inattentive-type and in older adolescents.
- Sallee 2009 (JAACAP, n=324, doses 1–4 mg): Intuniv beat placebo in children 12 and under, with no clear advantage in ages 13–17.
The practical read: guanfacine's monotherapy evidence is strongest in younger children with hyperactive/combined-type ADHD. For an inattentive teenager, the case is thinner.
Adult ADHD, off-label, one trial. Iwanami 2020 (J Clin Psychiatry, n=201, Japan) was a 12-week RCT titrating to 4–6 mg/day (mean 5 mg). ADHD-RS-IV scores fell 31→20 on guanfacine vs. 31→24 on placebo (p=0.0005), effect size ~0.5, comparable to atomoxetine, smaller than stimulants. Quality of life did not significantly improve. 20% discontinued for side effects (sedation, hypotension, dizziness). It was manufacturer-funded (Takeda). So: guanfacine works in adults, modestly, at a real dropout cost.
Adjunct to a stimulant, the sweet spot. McCracken 2016 (JAACAP, n=207, ages 7–14) compared stimulant alone, guanfacine alone, and the combination. The combination beat either monotherapy. It produced less blood-pressure elevation than the stimulant alone and less fatigue than guanfacine alone. The benefits were real but not large, and neither drug fully cancelled the other's side effects, but there was no meaningful downside. If a patient is on a stimulant and needs more coverage (or is bothered by stimulant-driven blood-pressure elevation), adding guanfacine is well-supported.
Reasonable Off-Label Niches
These are areas where guanfacine (or its cousin clonidine) is used clinically, mostly on weaker evidence:
- Tic disorders: alpha-2 agonists suppress tics; useful when ADHD and tics coexist (a setting where stimulants are traditionally feared, though modern data suggest stimulants are safer for tics than once thought).
- ADHD + substance use disorder: no abuse potential, no striatal dopamine; a rational choice when a controlled substance is unwise.
- ADHD + bipolar disorder: small studies support alpha-2 agonist safety in bipolar illness; guanfacine does not carry the mania-induction concern that noradrenergic agents (atomoxetine, stimulants) do.
- Anxiety / agitation: dosed in the daytime for a calming effect.
- Opioid and alcohol withdrawal, nicotine cessation: alpha-2 agonists blunt autonomic withdrawal (clonidine has more evidence here).
- Autism-related irritability, borderline self-harm urges: small/adjunctive data, mostly clonidine.
- Symptom relief odds and ends: SSRI-induced sweating, clozapine-induced hypersalivation, hot flashes, restless legs.
Where Guanfacine Fails or Doesn't Belong
- PTSD. Do not use it. Two small randomized trials in veterans (Neylan 2006, Am J Psychiatry, mean dose 2.4 mg; Davis 2008) found guanfacine no better than placebo for PTSD, and Neylan reported more side effects (somnolence, lightheadedness, dry mouth). Prazosin (an alpha-1 blocker, different mechanism) is the alpha-adrenergic agent with randomized evidence for PTSD-related nightmares and sleep disturbance; its benefit for overall PTSD symptoms is borderline in pooled analyses, and the largest trial, in veterans, was negative.
- Monotherapy for uncomplicated ADHD in a stimulant-eligible patient: you're leaving efficacy on the table.
The cleanest way to decide is to ask, "Why not a stimulant?" If there's a good answer (bipolar disorder, addiction history, tics, a patient or family who refuses controlled substances, intolerable stimulant side effects), guanfacine moves up the list. If there's no good answer, a stimulant is the better first move, and guanfacine is best kept in reserve as an add-on.
Part 2: Workup and Candidacy
Guanfacine's workup is short and centers on the cardiovascular system, because it is an antihypertensive: it lowers heart rate and blood pressure.
Baseline Assessment
| Check | Why |
|---|---|
| Heart rate | Guanfacine causes bradycardia; establish a baseline you'll track at each titration |
| Blood pressure | It lowers BP; you want to know the starting point, especially in lean, young, or already-normotensive patients |
| Cardiac / syncope history | History of syncope, falls, orthostasis, or arrhythmia raises the stakes |
| Current antihypertensives | Additive hypotension/bradycardia; coordinate with the PCP |
| ECG | Not routine; obtain if there is baseline QTc concern, known cardiac disease, arrhythmia history, or in frail/elderly patients |
Who Is a Poor Candidate?
- Patients with a history of hypotension, syncope, or falls (the additive BP/HR drop can be dangerous).
- Baseline QTc prolongation or significant arrhythmia: guanfacine produced modest QTc prolongation in the adult trial.
- Frail or elderly patients, in whom bradycardia and hypotension are less well tolerated (and who were not represented in the pediatric-heavy trial base).
- Patients who need a rapid response: guanfacine takes 2–5 weeks to build; it is the wrong drug for someone who needs relief this week.
- Patients who cannot tolerate any sedation and cannot dose around it.
A patient already on an antihypertensive is not automatically excluded (most can continue both drugs with close BP monitoring and PCP coordination), but the combination demands attention.
Part 3: How to Start and Dose
Children 6–12 and teens 13–17ADHD, alone or with a stimulantFDA label1 mg once daily, up no more than 1 mg a week, to 0.05–0.12 mg/kg/day as tolerated. Above 4 mg/day is not evaluated at 6–12, above 7 mg/day at 13–17.In practiceTypical effective range 2–4 mg/day, dosed by weight where relevant; titrated weekly to effect.
Kidney or liver impairmentSignificant impairmentFDA labelMay need a lower dose in significant renal or hepatic impairment. No numeric change is given.In practiceSignificant impairment of either organ can raise exposure: start low, titrate cautiously, and watch for exaggerated low blood pressure and sedation.
With interacting drugsCYP3A4 inhibitors or inducersFDA labelCYP3A4 inhibitor (e.g., ketoconazole): half the dose. Inducer (e.g., carbamazepine): consider up to double. When stopped, return to usual.
When to take itTime of day and foodFDA labelOnce daily, morning or evening, at about the same time each day. Do not give with high-fat meals.In practiceEvening for daytime sedation; daytime for anxiety or agitation, including a low dose at 3 PM.
StoppingTaper; rebound blood pressureFDA labelDecrease by no more than 1 mg every 3–7 days, watching blood pressure and pulse.In practiceAbout 2 weeks, as used in the adult trial, is a reasonable default; slower is fine, including with cardiovascular risk.
Switching from Tenex (IR)Immediate-release to extended-releaseFDA labelStop the immediate-release tablet, then titrate Intuniv on the usual schedule. Do not substitute mg for mg.In practiceDo not assume milligram-for-milligram equivalence, or you will under- or over-dose.
Formulations
- Intuniv (extended-release): The FDA-approved, preferred formulation for ADHD. Once-daily dosing. Now available generically and affordably.
- Tenex (immediate-release): The older antihypertensive tablet. Effective but not the ADHD-preferred product; ER gives smoother levels and better tolerability.
- Half-life: 16–18 hours in adults (shorter in children), which is what makes reliable once-daily dosing feasible, a real advantage over clonidine, whose ~12-hour half-life often forces twice-daily dosing.
A bioavailability trap you must respect: at the same dose the ER form (Intuniv) has 43% lower bioavailability and 60% lower peak levels than the IR form. Do not substitute milligram for milligram when switching between Tenex and Intuniv: the label says to stop the IR tablet and titrate Intuniv on its own schedule.
Starting Dose and Titration
Children/adolescents (Intuniv ER)
- Start 1 mg once daily.
- Titrate by no more than 1 mg per week based on tolerability and response.
- Typical effective range 2–4 mg/day in lighter children (label table: 2–4 mg up to 41.4 kg, up to 7 mg from 58.5 kg). Doses above 4 mg/day have not been evaluated in children 6–12 (or studied with a stimulant), and doses above 7 mg/day have not been evaluated in adolescents 13–17.
- Dose by weight where relevant (pediatric labeling scales the target to weight; roughly 0.05–0.12 mg/kg/day territory), but in practice the weekly-titration-to-effect approach works.
Adults (off-label, per Iwanami)
- Start 2 mg/day, titrate 1 mg/week over ~5 weeks.
- Target 4–6 mg/day (mean achieved 5 mg/day). There is no FDA-approved adult dose; the label's ceilings (4 mg in children 6–12, 7 mg in adolescents 13–17) are pediatric.
The rule for everyone: start low, go up slowly, and let tolerability set the pace. Guanfacine's side effects (sedation, hypotension, dizziness) cluster during initiation and titration, are dose-related, and often ease with time. Rushing the titration is the main self-inflicted cause of dropout.
When to Dose
Time the dose to the effect you want:
- Daytime sedation is the problem: dose in the evening. The long half-life carries coverage into the next day while the sedative peak occurs during sleep.
- You're targeting anxiety or agitation: dose during the day to use the calming effect when it's needed.
Because the half-life is long, once-daily dosing (at whichever time suits the patient) is appropriate for most.
The Food Interaction
This one is specific to guanfacine, and you should counsel on it explicitly: a high-fat meal raises guanfacine ER exposure substantially, roughly a 75% jump in peak concentration (Cmax) and a 40% rise in total exposure (AUC). The consequence is more fatigue and hypotension. The fix is not "take it fasting" so much as consistency: take it the same way relative to food every day, and avoid dosing right after a heavy, fatty meal. (For contrast: clonidine ER and atomoxetine have no meaningful food interaction, which can be a reason to prefer them in a patient who can't keep meal timing consistent.)
Two dosing details separate a smooth guanfacine start from a miserable one: (1) titrate no faster than 1 mg/week, and (2) keep the relationship to food constant. A patient who ramps too fast and takes the drug after a big fatty dinner one night and on an empty stomach the next will have unpredictable sedation and blame the medication.
Part 4: Monitoring
Guanfacine requires no blood levels and no routine labs. The monitoring is cardiovascular and clinical.
| Timepoint | Check |
|---|---|
| Baseline | HR, BP; ECG if cardiac risk |
| At each dose increase | HR and BP (watch for bradycardia and hypotension) |
| Steady state / maintenance | Periodic HR and BP; more often in the elderly, the frail, or anyone on other antihypertensives |
| Throughout | Sedation severity and its functional impact; adjust timing/dose accordingly |
On the QTc: the adult RCT showed a modest QTc prolongation vs. placebo, and EKG changes were still detectable in ~2% of patients two weeks after discontinuation. This is not a reason to avoid the drug in a low-risk patient, but it does argue for a baseline ECG (and caution) in anyone with pre-existing QTc concern, known cardiac disease, or on other QT-prolonging agents.
Part 5: Side Effects and How to Manage Them
As with most alpha-2 agonists, side effects are dose-related, front-loaded to the titration period, and often ease with time. They are common enough, though, that tolerability, not efficacy, is the usual reason guanfacine gets stopped.
CNS: Sedation, Somnolence, Fatigue
This is guanfacine's defining liability. On monotherapy, somnolence (the label's term, covering somnolence, sedation and hypersomnia) ran 38% in the fixed-dose pediatric trials and 54–56% in the flexible-dose trials, against 11–23% on placebo. It is dose-related, rising from 28% at 1 mg to 51% at 4 mg. It is the single most common reason patients quit.
Management:
- Move the dose to the evening so the peak sedation lands during sleep.
- Slow the titration: much of the sedation eases over days to weeks if you don't rush.
- Reassure that it is dose-related and usually improves.
Cardiovascular: Hypotension, Bradycardia, QTc
Guanfacine is an antihypertensive; these effects are on-target, not idiosyncratic.
- Hypotension and dizziness drove much of the 20% dropout in the adult trial.
- Bradycardia: check the pulse, not just the cuff.
- QTc prolongation: modest, but real (see Monitoring).
Management:
- Titrate slowly: most cardiovascular symptoms are dose- and titration-related.
- Check HR/BP at every increase.
- Coordinate with the PCP if the patient is on antihypertensives; the effects are additive.
- Caution in the elderly and frail, in whom a drop in BP or HR is more consequential (falls, syncope).
- On discontinuation, taper to avoid rebound hypertension (see Part 6).
GI
- Constipation: manage with a standard bowel regimen (fluids, fiber, an osmotic laxative if needed).
- Dry mouth: common to the class; usually mild.
The Paradoxical Upside
Some of guanfacine's "side effects" are useful elsewhere. Its alpha-2 agonism means it can simultaneously relieve tics, SSRI-induced sweating, clozapine-induced hypersalivation, hot flashes, and restless legs. In a patient with ADHD plus one of these, guanfacine may earn double duty.
Do not tell a patient that guanfacine will be gentler than clonidine: the labels do not show a difference. In the fixed-dose trials, somnolence was 38% on guanfacine ER across all doses against 11% on placebo, and 31% on clonidine ER 0.4 mg/day and 38% on 0.2 mg/day against 4% on placebo (separate trials, and the labels do not compare the two drugs). Set the expectation that guanfacine is sedating, dose at night, and if the drowsiness is a dealbreaker, switch strategies rather than pushing a miserable patient to a higher dose.
Part 6: Overdose, Toxicity, and Discontinuation Safety
Guanfacine has no boxed warning. Its safety concerns are pharmacologically predictable extensions of an alpha-2 agonist antihypertensive.
Overdose
Overdose produces exaggerated on-target effects: bradycardia, hypotension, sedation/CNS depression (drowsiness progressing to lethargy). In children especially, ingestion can cause pronounced somnolence and bradycardia. Management is supportive: this is an ED evaluation with cardiac monitoring; there is no specific antidote and treatment is directed at hemodynamics and airway. Because guanfacine lowers heart rate and blood pressure, co-ingestion with other CNS depressants or antihypertensives compounds the risk.
Rebound Hypertension
This is the one to remember: abrupt discontinuation of an alpha-2 agonist can cause rebound hypertension. This is best documented with clonidine, but the mechanism (loss of central sympatholytic tone) plausibly applies to guanfacine, and the prudent assumption is that it does: guanfacine's longer half-life may soften but does not eliminate the risk.
Taper it. The adult RCT used a 2-week taper, which is a reasonable default. A patient who runs out and simply stops, which is common in the real world, can rebound; build the taper into the plan and warn the patient not to stop on their own.
QTc Persistence
To say it again: after stopping guanfacine, QTc changes lingered in ~2% of patients at two weeks. For most patients this is clinically irrelevant, but in anyone with cardiac risk or on other QT-prolonging drugs, keep it in mind around discontinuation as well as initiation.
Part 7: Drug Interactions
Guanfacine Is a CYP3A4 Substrate
Its levels are moved by CYP3A4:
- CYP3A4 inhibitors raise guanfacine levels: more sedation and hypotension. The psychiatric example is nefazodone, a strong CYP3A4 inhibitor; fluvoxamine inhibits CYP3A4 only moderately, its strong inhibition being of CYP1A2 and CYP2C19. Azole antifungals, macrolides, ritonavir and grapefruit belong on the same list, and the label's halving applies to moderate inhibitors as well as strong ones. Consider a lower guanfacine dose and monitor when co-prescribing.
- CYP3A4 inducers lower guanfacine levels: possible loss of efficacy. Carbamazepine is the classic psychiatric example (also phenytoin, rifampin, St. John's wort). You may need a higher guanfacine dose.
Mirtazapine
Mirtazapine is an alpha-2 antagonist, pharmacologically opposite to guanfacine. Case reports describe hypertensive urgency when the two are combined (Abo-Zena 2000). Avoid the combination or use it cautiously with close BP monitoring.
Additive Cardiovascular Depressants
- Other antihypertensives (beta-blockers, other alpha-2 agonists, calcium-channel blockers): additive hypotension/bradycardia. Combinable with monitoring and PCP coordination, but respect the additive effect.
- Other CNS depressants (alcohol, benzodiazepines, opioids, sedating antihistamines): additive sedation.
- Other QT-prolonging agents: additive QTc effect: factor guanfacine's modest contribution into a patient already on QT-prolonging drugs.
The Beneficial "Interaction": Stimulants
The most clinically important combination is a good one. In McCracken 2016 (n=207, 8 weeks, immediate-release guanfacine), guanfacine plus dexmethylphenidate beat either monotherapy on the ADHD-RS inattentive subscale and produced a higher CGI-I response rate. What the trial does not show is the stimulant cancelling guanfacine's sedation: sedation ran 22.9% on the combination against 17.6% on guanfacine alone, and the authors report sedation, somnolence, lethargy and fatigue as more common in both guanfacine arms. Appetite suppression was the side effect the combination did soften, 35.7% against 44.9% on the stimulant alone. Guanfacine is the preferred agent for augmenting a stimulant, with better trial evidence than atomoxetine (whose safety combined with stimulants is less established).
Part 8: Special Populations
Pregnancy and Lactation
Human data are limited. There is no strong signal of major teratogenicity, but the evidence base is thin, and guanfacine is not a drug with a reassuring pregnancy dataset. Weigh the benefit against the modest efficacy: ADHD is rarely an emergency that mandates pharmacotherapy in pregnancy, so for many patients the reasonable move is to defer or minimize. If treatment is necessary, individualize with the obstetric team, and remember the maternal cardiovascular effects (hypotension, bradycardia). Lactation data are sparse; decide case-by-case with pediatric input. Do not represent guanfacine as "known safe" in pregnancy or breastfeeding; the honest answer is "insufficiently studied."
Elderly / Frail
Guanfacine's trial base is overwhelmingly pediatric. In older or frail patients, the cardiovascular effects (bradycardia, hypotension, QTc prolongation, fall risk) carry more weight and are less well characterized. Start lower, go slower, monitor HR/BP closely, and consider a baseline ECG. Often not the best choice in this population.
Renal / Hepatic
The label gives no numeric adjustment, only that a dose reduction may be necessary in significant renal or hepatic impairment. Guanfacine is cleared by both liver and kidney, with roughly half of its clearance hepatic, so impairment of either can raise exposure: start low, titrate cautiously, and monitor for exaggerated hypotension/sedation. Coordinate with the relevant specialist for advanced organ impairment.
Pediatric
This is guanfacine's FDA home (ages 6–17). Efficacy is best supported in younger children with hyperactive/combined-type ADHD; the signal weakens in inattentive-type and in adolescents. Half-life is shorter in children than adults, which can matter for dosing coverage. The alpha-2 agonists (guanfacine, clonidine) have small studies supporting safety in the psychiatrically comorbid child (bipolar illness, autism irritability), an advantage over atomoxetine's noradrenergic mania concern.
Part 9: Discontinuation
Guanfacine is simpler to stop than lithium or an antidepressant, but it is not a stop-anytime drug because of the rebound-hypertension risk.
- Taper, don't stop abruptly. A ~2-week taper (as used in the adult trial) is a reasonable default; slower is fine, especially in patients on higher doses or with cardiovascular risk.
- Monitor BP through and just after the taper: rebound hypertension is the specific hazard.
- If ADHD symptoms were the target and you're switching agents, there's no psychiatric withdrawal syndrome to fear (unlike lithium's rebound mania); the concern is purely cardiovascular.
Part 10: Guanfacine vs. the Alternatives
vs. Stimulants
Stimulants win on efficacy (effect size 0.8–0.9 vs. guanfacine's ~0.5) and speed (rapid vs. 2–5 weeks). Guanfacine wins on abuse potential (none vs. real), controlled-substance status (unscheduled, refillable vs. Schedule II), and suitability in specific comorbidities stimulants worsen. It's calming rather than activating. The two are not really competitors so much as tools for different situations, and they combine well.
vs. Clonidine (Kapvay)
The other alpha-2 agonist. Roughly equal efficacy for ADHD. Guanfacine's advantage: a longer half-life (16–18 h vs. 12 h, for easier once-daily dosing). The labels do not show a difference in sedation (see the sedation figures under side effects). Clonidine's advantages: more research in psychiatric comorbidities (PTSD, mania, BPD, autism irritability), a transdermal patch option, and no food interaction. For a straightforward ADHD patient who would do better with once-daily dosing, guanfacine is the natural switch; for a patient where the comorbidity is the main event, clonidine may have more supporting data.
vs. Atomoxetine (Strattera)
Similar effect size (~0.5 vs. 0.4–0.6). Both are non-controlled, non-abusable. Differences: atomoxetine is noradrenergic (raises HR/BP, carries a pediatric suicidality warning, and has a theoretical mania-induction risk that makes it a poor choice in bipolar illness) while guanfacine is sympatholytic (lowers HR/BP, calming, benign in bipolar illness). Atomoxetine's interactions run through CYP2D6 (fluoxetine, paroxetine, bupropion, poor metabolizers); guanfacine's through CYP3A4. Choose by the comorbidity: bipolar disorder or a need for calming favors guanfacine; comorbid anxiety or a need to avoid sedation/hypotension often favors atomoxetine.
It sits in an awkward middle: not strong enough to be first-line, not distinctive enough to be reached for reflexively. It is a specialist's tool, the answer to "my ADHD patient can't or shouldn't take a stimulant, and here's the comorbidity that tells me which non-stimulant to pick."
Mechanism
Guanfacine is a selective alpha-2A adrenergic agonist. By stimulating central alpha-2A receptors it reduces sympathetic nerve impulses from the vasomotor center to the heart and blood vessels, lowering peripheral vascular resistance and heart rate (its original antihypertensive action).
Its ADHD benefit is a prefrontal-cortex story. By stimulating postsynaptic alpha-2A receptors on prefrontal pyramidal neurons, guanfacine strengthens the neural signals underlying working memory, attention regulation, and impulse control; in Amy Arnsten's model, it "closes" the ion channels that otherwise leak away the network connectivity these neurons need. This is the opposite end of the mechanism from stimulants, which flood the synapse with catecholamines; guanfacine instead makes existing prefrontal signaling more efficient. The Intuniv label itself says the mechanism of action of guanfacine in ADHD is not known.
Two mechanistic facts explain the clinical feel of the drug: the alpha-2A action is why it is calming rather than activating (and useful for anxiety, tics, and withdrawal states), and its slow, tonic strengthening of prefrontal circuits is why the benefit builds over 2–5 weeks rather than switching on like a stimulant.
Pharmacokinetics: half-life 16–18 h in adults (shorter in kids); CYP3A4-metabolized; ER bioavailability 60–75% of IR (3 mg IR ≈ 4 mg ER); absorption meaningfully increased by high-fat meals.
The Bedside Cheat Sheet
Where it fits
- Third-line ADHD monotherapy (effect size ~0.5 vs. stimulants 0.8–0.9); at its best as a stimulant adjunct or in ADHD + comorbidity (bipolar, addiction, tics, anxiety, sleep problems)
- Non-controlled, non-abusable, calming not activating. Takes 2–5 weeks to work
- Not for PTSD (failed RCTs); prazosin is the alpha agent with evidence for PTSD nightmares
Starting
- Intuniv ER, start 1 mg once daily in children, titrate by no more than 1 mg/week
- Ages 6–17: target 0.05–0.12 mg/kg/day by weight (1–7 mg/day; 2–4 mg for a 34 kg child, up to 7 mg from 58.5 kg); above 4 mg/day not evaluated at ages 6–12 or studied with a stimulant, above 7 mg/day not evaluated at 13–17. Adults (off-label): start 2 mg/day, target 4–6 mg/day
- IR to ER: don't switch milligram-for-milligram; stop the IR and titrate Intuniv on its own schedule (label)
- Dose in the evening for daytime sedation; daytime for anxiety/agitation
- Keep food timing consistent: high-fat meals raise levels ~75% (Cmax) / 40% (AUC)
Monitoring
- HR and BP at baseline and every dose increase. No blood levels, no routine labs
- ECG only if cardiac risk / QTc concern / elderly
Side effects & don't forget
- Sedation is the big one (38–56% monotherapy vs 11–23% placebo): evening dosing and slow titration. Adding a stimulant does not reliably reduce it
- Hypotension, bradycardia, dizziness: titrate slowly, check vitals, coordinate with PCP on antihypertensives
- Modest QTc prolongation (persisted in ~2% two weeks after stopping). Constipation, dry mouth. Bonus: relieves tics, sweating, sialorrhea, hot flashes, RLS
- Taper by no more than 1 mg every 3 to 7 days (label): rebound hypertension with abrupt stop. CYP3A4 substrate: nefazodone and the azoles raise it, carbamazepine lowers it. Mirtazapine (opposite alpha-2 action): hypertensive-urgency reports, avoid/caution
Guanfacine will never be the most effective ADHD drug. Its value is situational and specific: a non-abusable, non-controlled, calming agent that can be given to the patient for whom a stimulant is wrong (the one with bipolar disorder, the one in recovery, the one with tics, the one whose family won't accept a Schedule II prescription), and a useful partner to a stimulant when one drug alone isn't enough. Start it at 1 mg, climb by no more than 1 mg a week, keep an eye on the pulse and the pressure, time the dose to fight the sedation, and taper it when you stop.