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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Central alpha-2 Adrenergic Agonist [EPC]
Guanfacine is a central alpha-2 adrenergic agonist used primarily for the treatment of ADHD and hypertension. It works by stimulating receptors in the brain to reduce sympathetic nervous system activity and improve cognitive control.
Name
Guanfacine
Raw Name
GUANFACINE HYDROCHLORIDE
Category
Central alpha-2 Adrenergic Agonist [EPC]
Salt Form
Hydrochloride
Drug Count
8
Variant Count
124
Last Verified
February 17, 2026
RxCUI
862006, 862013, 862019, 862025, 197745, 197746, 862010, 862015, 862021, 862027, 1092566, 1092567
UNII
PML56A160O, 30OMY4G3MK
About Guanfacine
Guanfacine is a central alpha-2 adrenergic agonist used primarily for the treatment of ADHD and hypertension. It works by stimulating receptors in the brain to reduce sympathetic nervous system activity and improve cognitive control.
Detailed information about Guanfacine
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Guanfacine.
The Food and Drug Administration (FDA) first approved the immediate-release formulation of guanfacine in 1986 for the management of hypertension. Later, in 2009, the FDA approved the extended-release formulation for the treatment of ADHD in children and adolescents aged 6 to 17 years. This approval marked a significant shift in ADHD management, providing a viable alternative for patients who do not tolerate stimulants or for whom stimulants are contraindicated. According to the FDA-approved labeling (2024), guanfacine can be used as monotherapy or as adjunctive therapy to stimulant medications.
The mechanism of action for guanfacine is multifaceted, depending on the condition being treated. At the molecular level, guanfacine is a selective agonist for alpha-2A adrenergic receptors. These receptors are found in high concentrations in the prefrontal cortex (PFC), an area of the brain responsible for executive functions, including impulse control, working memory, and attention.
In the context of ADHD, guanfacine is thought to strengthen the 'signal' of neurons in the prefrontal cortex. It binds to post-synaptic alpha-2A receptors on the dendritic spines of PFC neurons. This binding inhibits the production of cyclic adenosine monophosphate (cAMP), which in turn closes hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. By closing these channels, guanfacine enhances the connectivity of the PFC networks, improving the patient's ability to focus and resist distractions. This 'strengthening' of the prefrontal cortex is fundamentally different from the 'increasing' of neurotransmitter levels seen with stimulant medications.
For hypertension, guanfacine acts on alpha-2 receptors in the medulla oblongata (the brain's vasomotor center). By stimulating these receptors, guanfacine reduces the outflow of sympathetic nerve impulses from the brain to the heart and blood vessels. This results in a decrease in peripheral vascular resistance, a reduction in heart rate, and a subsequent lowering of blood pressure. Because it is highly selective for the alpha-2A subtype, it typically produces fewer side effects (such as sedation) compared to older, non-selective agonists like clonidine.
Understanding the pharmacokinetics of guanfacine is essential for safe prescribing and patient management. The drug exhibits distinct characteristics based on whether the immediate-release (IR) or extended-release (ER) formulation is used.
Guanfacine is FDA-approved for two primary indications:
Off-label uses, which are common in clinical practice but not FDA-sanctioned, include:
Guanfacine is available in the following oral dosage forms:
> Important: Only your healthcare provider can determine if Guanfacine is right for your specific condition. Never start or stop this medication without professional medical advice.
For the treatment of Hypertension, the standard starting dose of immediate-release guanfacine is 1 mg taken daily at bedtime. Taking the dose at bedtime helps minimize the impact of daytime somnolence (drowsiness). If blood pressure control is not achieved after 3 to 4 weeks, your healthcare provider may increase the dose to 2 mg daily. While doses up to 3 mg have been studied, higher doses are associated with a significant increase in side effects without a proportional increase in efficacy.
For ADHD in Adults (off-label use), clinicians may prescribe the extended-release formulation starting at 1 mg per day, gradually titrating upward by 1 mg increments per week until a target dose (usually 2 mg to 4 mg) is reached, based on clinical response and tolerability.
Guanfacine extended-release (Intuniv) is FDA-approved for ADHD in children and adolescents (ages 6 to 17). Dosing is typically weight-based and follows a strict titration schedule:
In patients with significant renal impairment, the clearance of guanfacine is reduced. Healthcare providers may need to reduce the dosage or increase the dosing interval. Close monitoring of blood pressure and heart rate is mandatory in this population.
Since guanfacine is metabolized by the liver, patients with hepatic insufficiency should be monitored closely. While specific dose-reduction guidelines for hepatic impairment are not always standardized, a lower starting dose and slower titration are generally recommended.
Older adults (65+) may be more sensitive to the hypotensive and sedative effects of guanfacine. Clinicians usually start at the lowest possible dose and monitor for orthostatic hypotension (dizziness upon standing) and fall risks.
If you miss a dose of guanfacine, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and resume your regular schedule. Do not double the dose to catch up. If you miss two or more consecutive doses, contact your healthcare provider, as a re-titration (starting back at a lower dose) may be necessary to avoid side effects.
Signs of guanfacine overdose include severe drowsiness, lethargy, bradycardia (slow heart rate), hypotension (low blood pressure), and miosis (constricted pupils). In severe cases, respiratory depression or coma can occur. If an overdose is suspected, contact a Poison Control Center or seek emergency medical attention immediately. Treatment is primarily supportive, focusing on maintaining heart rate and blood pressure.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop taking the medication without medical guidance, as sudden discontinuation can cause a dangerous spike in blood pressure.
The most frequently reported side effects of guanfacine, particularly during the initial titration phase, include:
> Warning: Stop taking Guanfacine and call your doctor immediately if you experience any of these serious symptoms:
Long-term use of guanfacine requires ongoing monitoring. Potential long-term considerations include:
No FDA black box warnings currently exist for Guanfacine. However, the FDA does mandate strong warnings regarding the risk of hypotension, bradycardia, and the dangers of abrupt discontinuation.
Report any unusual symptoms or side effects to your healthcare provider immediately. Your doctor may adjust your dose or suggest ways to manage side effects, such as taking the medication at bedtime or ensuring better hydration.
Guanfacine is a potent medication that affects the central nervous system and the cardiovascular system. It is vital that patients and caregivers understand the risks associated with its use. The primary safety concerns involve its effects on blood pressure and heart rate, as well as its sedative properties. Patients should be screened for pre-existing heart conditions before starting therapy.
As of 2026, there are no FDA black box warnings for Guanfacine. However, the absence of a black box warning does not imply the drug is without risk. Clinical guidelines emphasize the need for careful monitoring of cardiovascular parameters.
Before starting guanfacine and periodically during treatment, healthcare providers should perform the following:
Patients should be cautioned against driving, operating heavy machinery, or engaging in hazardous activities until they are certain that guanfacine does not make them excessively drowsy or dizzy. This is especially critical during the first few weeks of treatment or after a dose increase.
Alcohol should be strictly avoided while taking guanfacine. Alcohol significantly enhances the sedative effects of the drug and can lead to dangerous levels of respiratory depression or profound hypotension.
When stopping guanfacine, the dose must be tapered gradually. A common tapering schedule involves reducing the daily dose by no more than 1 mg every 3 to 7 days. Patients should be monitored for signs of withdrawal, including nervousness, rapid heart rate, and headache.
> Important: Discuss all your medical conditions, especially heart rhythm problems, kidney disease, or a history of fainting, with your healthcare provider before starting Guanfacine.
There are few absolute contraindications for drug combinations, but the following carry extreme risk:
Guanfacine is not known to significantly interfere with most common laboratory tests. However, it may cause a slight increase in plasma growth hormone levels or a decrease in urinary catecholamines, which could affect tests for certain rare endocrine tumors (like pheochromocytoma).
> Important: Tell your doctor about ALL medications, vitamins, and herbal products you are taking. A complete list is necessary to prevent dangerous drug-drug interactions.
In these cases, the healthcare provider must perform a careful risk-benefit analysis:
There is a potential for cross-sensitivity between guanfacine and other alpha-2 adrenergic agonists, such as clonidine (Catapres) or tizanidine (Zanaflex). If a patient has had a severe reaction to one drug in this class, the others should be used with extreme caution or avoided entirely.
> Important: Your healthcare provider will evaluate your complete medical history, including any heart conditions or previous drug allergies, before prescribing Guanfacine.
Guanfacine is classified under the older FDA Pregnancy Category B. This means that animal reproduction studies have failed to demonstrate a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. According to data available in 2024, guanfacine should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. It is not known to be a teratogen (causing birth defects) in humans, but its effects on fetal neurodevelopment have not been extensively studied.
It is unknown whether guanfacine is excreted in human milk. However, because many drugs are excreted in breast milk and because of the potential for serious adverse reactions in nursing infants (such as sedation or low blood pressure), a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Guanfacine ER is well-established for use in children and adolescents (ages 6-17) for ADHD. It is not recommended for children under the age of 6, as safety and efficacy have not been established in this age group. In pediatric patients, the most significant concerns are somnolence and the potential for weight gain. Long-term studies (up to 2 years) have shown that guanfacine is generally safe, but growth and cardiovascular health must be monitored.
Clinical studies of guanfacine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. However, because elderly patients are more likely to have decreased renal function and are more susceptible to orthostatic hypotension and falls, they should be started on the lowest possible dose. The risk of sedation is also higher in this population.
In patients with end-stage renal disease or significant impairment, the clearance of guanfacine is significantly reduced. While the drug is not easily removed by hemodialysis, the starting dose should be low (e.g., 1 mg), and titration should be very slow. Monitoring for toxicity (extreme lethargy, very low BP) is essential.
Patients with Child-Pugh Class B or C hepatic impairment may have reduced clearance of guanfacine. While specific dose-adjustment tables are not provided by manufacturers, clinicians typically use a 'start low, go slow' approach to avoid accumulation of the drug.
> Important: Special populations require individualized medical assessment. Always inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
Guanfacine is a selective agonist for the alpha-2A adrenergic receptor. It has a 15- to 20-fold higher affinity for the alpha-2A subtype compared to the alpha-2B or alpha-2C subtypes. In the brain, these receptors are coupled to inhibitory G-proteins (Gi). When guanfacine binds to these receptors in the prefrontal cortex, it inhibits the enzyme adenylyl cyclase, which leads to a decrease in the production of intracellular cAMP. This biochemical change leads to the closure of HCN channels (hyperpolarization-activated cyclic nucleotide-gated channels) on the dendrites of neurons. This process effectively 'strengthens' the synaptic connection, improving the signal-to-noise ratio in the prefrontal cortex, which translates to improved attention and impulse control.
The pharmacodynamic effects of guanfacine include a reduction in sympathetic tone and an increase in parasympathetic tone. This results in a decrease in heart rate and blood pressure. Unlike clonidine, guanfacine is less likely to cause a 'rebound' effect if a single dose is missed, due to its longer half-life, though chronic discontinuation still poses a risk. The onset of action for hypertension is typically within 1-2 weeks of consistent use, while the full therapeutic effect for ADHD may take 2 to 4 weeks to manifest.
| Parameter | Value |
|---|---|
| Bioavailability | ~80% (IR); ~58% (ER) |
| Protein Binding | ~70% (primarily Albumin) |
| Half-life | 10–30 hours (Adults); ~14-18 hours (Pediatrics) |
| Tmax | 1–4 hours (IR); ~5 hours (ER) |
| Metabolism | Hepatic (CYP3A4) |
| Excretion | Renal (50% unchanged), Fecal (minor) |
Guanfacine is classified as a central alpha-2 adrenergic agonist. Related medications in this class include clonidine (Catapres), methyldopa (Aldomet), and tizanidine (Zanaflex). Within the ADHD therapeutic area, it is considered a 'non-stimulant' along with atomoxetine (Strattera) and viloxazine (Qelbree).
Medications containing this ingredient
Common questions about Guanfacine
Guanfacine is primarily used for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD) in children and adolescents, and for the management of hypertension (high blood pressure) in adults. In ADHD, it helps improve focus, reduce impulsivity, and manage hyperactivity by strengthening connections in the prefrontal cortex of the brain. For hypertension, it works by relaxing blood vessels and slowing the heart rate through its action on the central nervous system. It is often prescribed when stimulant medications are not tolerated or do not provide sufficient relief. Some doctors also use it off-label for tic disorders, anxiety, or sleep issues associated with ADHD.
The most common side effects of guanfacine include sleepiness (somnolence), dry mouth, tiredness, headache, and abdominal pain. Somnolence is particularly frequent, affecting more than one-third of patients, especially during the first few weeks of treatment or when the dose is increased. Patients may also experience a decrease in blood pressure and heart rate, which can lead to dizziness or lightheadedness. Most of these side effects are dose-dependent and tend to diminish as the body adjusts to the medication. It is important to stay hydrated and avoid taking the medication with high-fat meals to minimize these risks.
No, you should not drink alcohol while taking guanfacine. Alcohol significantly increases the sedative effects of guanfacine, which can lead to extreme drowsiness, impaired coordination, and slowed reaction times. Furthermore, both alcohol and guanfacine can lower blood pressure, and combining them may cause a dangerous drop in pressure, leading to fainting or cardiovascular distress. This interaction is particularly dangerous when driving or operating machinery. Always consult your healthcare provider about your lifestyle habits before starting this medication.
The safety of guanfacine during pregnancy has not been established through comprehensive clinical trials in humans. Animal studies have not shown direct harm to the fetus, but because human data is lacking, it is generally only used if the benefits to the mother clearly outweigh the potential risks to the unborn baby. It is categorized as a drug that requires caution, and pregnant women should discuss alternative treatments with their doctors. If you become pregnant while taking guanfacine, do not stop the medication abruptly, as this can cause rebound hypertension; instead, contact your doctor immediately for a tapering plan.
The time it takes for guanfacine to work depends on the condition being treated. For ADHD, some patients may notice a slight improvement in symptoms within the first week, but the full therapeutic effect usually takes 2 to 4 weeks of consistent dosing. This is because the medication works by gradually modulating brain receptors and strengthening neural pathways. For hypertension, blood pressure lowering effects typically begin within a few days, but it may take 1 to 2 weeks to reach a stable, optimal level. Patience and consistent adherence to the prescribed schedule are key to the drug's success.
No, you must never stop taking guanfacine suddenly. Abruptly discontinuing this medication can cause a 'rebound' effect, where your blood pressure and heart rate spike rapidly to dangerously high levels. This can lead to symptoms like severe headache, nervousness, tremors, and in rare cases, a hypertensive crisis. If you need to stop the medication, your healthcare provider will provide a tapering schedule to slowly reduce the dose over several days or weeks. Always follow your doctor's instructions for stopping any long-term medication.
If you miss a dose of guanfacine, take it as soon as you remember, unless it is nearly time for your next scheduled dose. If it is almost time for the next dose, skip the missed one and continue with your regular routine. Never take two doses at once to make up for a missed one, as this increases the risk of severe low blood pressure and sedation. If you miss more than two doses in a row, contact your doctor, as you may need to restart at a lower dose to avoid side effects during the re-titration process.
Weight gain is a possible side effect of guanfacine, though it is less common than the weight loss often seen with stimulant medications used for ADHD. In some clinical trials, a small percentage of pediatric patients experienced an increase in weight or body mass index (BMI) over long-term use. This may be due to the drug's sedative effects leading to decreased physical activity or changes in metabolic rate. Healthcare providers typically monitor a child's weight and growth during regular check-ups to ensure they remain within healthy ranges. If you notice significant or rapid weight changes, discuss them with your doctor.
Guanfacine can be taken with other medications, but there are many potential interactions that require careful management. It is frequently used alongside stimulants for ADHD to provide better symptom control. However, it should be used cautiously with other blood pressure medications, sedatives, or drugs that affect the CYP3A4 liver enzyme (like certain antibiotics or antifungals). Because of the risk of additive effects on heart rate and sedation, your doctor needs a complete list of all prescriptions, over-the-counter drugs, and supplements you are taking to ensure safety.
Yes, guanfacine is available as a generic medication in both immediate-release and extended-release forms. The generic versions are bioequivalent to the brand-name drugs Tenex (immediate-release) and Intuniv (extended-release). Generic versions are typically much more affordable than brand-name versions and are widely covered by most insurance plans. When switching from a brand-name to a generic, or between different generic manufacturers, ensure that you are still taking the correct formulation (extended-release vs. immediate-release), as they are not interchangeable at the same dose.