[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [ADHD medicines](https://durgical.com/en/pharmacology/classes/adhd-medicines/) › Guanfacine

# Guanfacine

## ADHD medicines?

ADHD medicines

A central alpha-2A agonist: a non-stimulant for ADHD (extended-release) and an older antihypertensive. Causes sleepiness and low blood pressure.

Updated Nov 1, 2026

## Quick facts

**Group**
[ADHD medicines](https://durgical.com/en/pharmacology/classes/adhd-medicines/)

**Target**
Alpha-2A adrenergic receptor (agonist)

**Used for**
ADHD · Hypertension

**Key effects**
Sleepiness · Low blood pressure · Dry mouth

**Monitor**
Sleepiness · Signs of rebound when stopping

**ATC**
C02AC02

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◎**Alpha-2A adrenergic receptor (agonist)**Guanfacine

ⓘ No guanfacine-bound structure exists. The figure shows dexmedetomidine, another alpha-2 agonist, in the agonist pocket of the human alpha-2A receptor (with its G protein), where guanfacine also binds.

**Target in 3D:** Alpha-2A adrenergic receptor (agonist). PDB structure 7EJA (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/7EJA) · Drag to rotate · pinch to zoom

Guanfacine stimulates alpha-2A adrenergic receptors. In the brainstem this lowers sympathetic outflow to the heart and vessels, so blood pressure and heart rate fall. In the prefrontal cortex, alpha-2A stimulation is thought to strengthen the networks for attention and impulse control, which is the basis of its use in ADHD. It is more selective for alpha-2A than clonidine.

- Guanfacine activates alpha-2A receptors
- Brainstem: less sympathetic outflow, lower blood pressure and heart rate
- Prefrontal cortex: better attention and impulse control
- Stopping suddenly can cause rebound hypertension

## Indications

- ADHD (extended-release), alone or added to a stimulant [Attention-deficit/hyperactivity disorder (ADHD) →](https://durgical.com/en/conditions/attention-deficit-hyperactivity-disorder/)
- Hypertension (immediate-release) [Arterial hypertension →](https://durgical.com/en/conditions/arterial-hypertension/)

## Adverse effects

### Common

- Sleepiness, fatigue and lethargy
- Low blood pressure, dizziness and slow heart rate
- Dry mouth, abdominal pain, nausea
- Irritability and insomnia

### Serious (rare, important)

- Rebound hypertension (even hypertensive encephalopathy) after abrupt stopping
- Syncope from hypotension and bradycardia
- Worsening of sinus node dysfunction or AV block

## Contraindications

- Hypersensitivity to guanfacine

## Key interactions

**Strong or moderate CYP3A4 inhibitors (ketoconazole, clarithromycin)**
Higher guanfacine exposure: more sedation and hypotension

**Strong or moderate CYP3A4 inducers (rifampicin, carbamazepine)**
Lower levels and loss of effect

**Alcohol, sedatives and other CNS depressants**
Additive sedation

**Other drugs that lower heart rate or blood pressure**
Additive bradycardia and hypotension

## What is monitored

- Heart rate and blood pressure before starting, after each change and periodically
- Sleepiness
- Signs of rebound when stopping

## Administration and safety

- Extended-release tablets are swallowed whole, not crushed, chewed or broken
- Extended-release tablets are not given with a high-fat meal
- Stopping is done by gradual tapering, never abruptly

## Pregnancy and breastfeeding

Decades of use have not shown a clear risk of birth defects, but experience in pregnancy is limited.

## Nursing care

- Measures heart rate and blood pressure before starting and after each change
- Teaches the family not to stop it suddenly and to avoid dehydration and overheating
- Warns about sleepiness before driving, cycling or other risky activities
- Asks about fainting and dizziness when standing up

## Pharmacokinetics

**Absorption**
Taken by mouth; the extended-release tablet is not interchangeable with the immediate-release one

**Metabolism**
Liver, mainly by CYP3A4

**Half-life**
About 17 hours (immediate-release), shorter in young people

## Memory aid

«GuanFACINE calms the FACE of the cortex»: an alpha-2A brake for ADHD; never pull the brake off suddenly or the pressure jumps back.

## Test yourself

Think of the answer, then tap the question to see it.

## Which receptor does guanfacine stimulate, and how does it lower blood pressure?

The alpha-2A adrenergic receptor; it reduces sympathetic outflow from the brainstem.

## What happens if guanfacine is stopped abruptly?

Rebound hypertension, which can be severe.

## Which two common side effects most often limit guanfacine in ADHD?

Sleepiness and low blood pressure (with slow heart rate).

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/guanfacine/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 3

- [Clonidine](https://durgical.com/en/pharmacology/clonidine/)
- [Atomoxetine](https://durgical.com/en/pharmacology/atomoxetine/)
- [Methylphenidate](https://durgical.com/en/pharmacology/methylphenidate/)

## Related conditions 2

- [Attention-deficit/hyperactivity disorder (ADHD)](https://durgical.com/en/conditions/attention-deficit-hyperactivity-disorder/)
- [Arterial hypertension](https://durgical.com/en/conditions/arterial-hypertension/)

[← Back to the class: ADHD medicines](https://durgical.com/en/pharmacology/classes/adhd-medicines/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - GUANFACINE tablet, extended release](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3a171942-37af-430d-8b9d-bb678ca2be4b) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - GUANFACINE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4248d53e-4dc3-452b-96f8-5d715c254c26) (DailyMed (U.S. National Library of Medicine), 2026); [Guanfacine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a601059.html) (MedlinePlus (U.S. National Library of Medicine), 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/guanfacine/