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Common guanfacine side effects and safety tips

Guanfacine side effects include drowsiness, dry mouth, and dizziness. Find out what to watch for and when to seek care while taking the drug.

August 21, 2026

By the Headway Editorial Team • Clinically reviewed by Bettina D'Andrea, MSN PMHNP-BC

7 min read

By the Headway Editorial Team • Clinically reviewed by Bettina D'Andrea, MSN PMHNP-BC

A new medication comes with plenty of questions, and guanfacine is no exception. Maybe you noticed a little drowsiness or dizziness in your first week and you're wondering whether that's normal. Maybe your child was just prescribed the brand-name drug Intuniv for attention-deficit/hyperactivity disorder (ADHD) and you want to know what to watch for before the first dose. It helps to know which guanfacine side effects are common and usually temporary, and which ones deserve a call to your prescriber. That knowledge can make the whole thing feel a lot more manageable.

This guide covers the side effects people most often notice when taking guanfacine for ADHD, the more serious risks to keep on your radar, and practical steps for taking it safely. Whether the prescription is for you or your child — or you're an adult still figuring out what your ADHD symptoms mean — you'll know what to expect and when to reach out for help.

Key insights

1

Guanfacine is a medication that helps lower blood pressure, and is prescribed for children and teens to treat ADHD.

2

Common side effects include drowsiness, dry mouth, dizziness, headache, constipation, and upset stomach. Not everyone who takes guanfacine experiences side effects. If side effects do appear, they usually lessen over time.

3

If you notice side effects don’t go away for a long period of time, or if they worsen, contact your healthcare provider right away. If you experience severe reactions like fainting or very low blood pressure, call 911.

What is guanfacine used for?

Guanfacine is a prescription medication that comes in two forms, and the one you're taking shapes what side effects to expect. The extended-release version, guanfacine ER (brand name Intuniv), is approved to treat ADHD in children and teens ages 6 to 17, either on its own or alongside a stimulant medication. The immediate-release version, guanfacine IR (brand name Tenex), is used to help manage high blood pressure. This guide focuses on guanfacine as prescribed for ADHD.

Guanfacine ER is FDA-approved for ADHD in children and adolescents. It is also prescribed off-label to adults with ADHD and can be used safely in adults when prescribed and monitored appropriately.

Unlike stimulant ADHD medications, guanfacine is a non-stimulant. It belongs to a class of medications called centrally acting alpha-2A adrenergic receptor agonists — a mouthful that simply means it works on receptors in the brain. For ADHD, it's thought to act on the part of the brain that supports attention and impulse control. Because it also lowers blood pressure and heart rate, several of its side effects tie back to those same effects on the body.

Common guanfacine side effects

Like many mental health medications, guanfacine can take time to reach its full effect, and side effects sometimes appear before the benefits do. The good news: Most are mild and ease up within the first few weeks as your body adjusts. Here are the ones people report most often, along with what tends to help.

Drowsiness and fatigue

Drowsiness and low energy are among the most common side effects, especially in the first days of treatment or right after a dose increase. For many people, it fades as the body adjusts. It can help to take guanfacine at the time of day your prescriber recommends.

Dry mouth

A dry, sticky mouth is common early on. It can help to sip water throughout the day, chew sugar-free gum, or use sugar-free lozenges.

Dizziness and low blood pressure

Because guanfacine lowers blood pressure and slows heart rate, some people feel dizzy or lightheaded, particularly when standing up quickly. This tends to lessen as treatment continues and your body adjusts to the medication.

Headache

Headaches can show up in the early weeks and usually pass on their own. If one lingers or gets worse, mention it to the healthcare provider who prescribed guanfacine for you.

Constipation and stomach upset

Constipation, stomach pain, or general stomach upset can happen, too. It can help to stay hydrated, eat fiber-rich foods, and stay active to keep things moving.

Less often, guanfacine can cause weakness, changes in mood or irritability, or sexual difficulties. A rash, trouble breathing, or swelling of the face, lips, or tongue could signal an allergic reaction — get emergency care right away if that happens. In the rare case of a suspected overdose, treat it as an emergency; the warning signs and what to do are covered below. And if any side effect sticks around or gets worse, that's worth a conversation with the provider who prescribed it.

Serious risks and warnings

Be sure to tell your provider if you take medication for high blood pressure or any other medication that lowers your blood pressure or heart rate. Guanfacine can also lower blood pressure and heart rate, so taking these medications together may increase the risk of dizziness, fainting, a slow heart rate, or low blood pressure. Your provider may need to monitor your blood pressure and heart rate more closely.

Guanfacine is generally well tolerated when it's taken as prescribed, but a few risks are worth understanding before and during treatment.

Rebound hypertension

If you stop guanfacine abruptly, your blood pressure and heart rate can spike — an effect known as rebound hypertension. To lower that risk, prescribers reduce the dose gradually over time rather than stopping all at once. An important note: Do not stop or change your dose on your own — talk with your prescribing provider first.

Drug and alcohol interactions

Alcohol and other medications that cause drowsiness, including certain sleep aids, allergy medicines, and sedatives, can intensify guanfacine's sedative effects. Give your prescriber and pharmacist a full list of everything you take, including over-the-counter products and supplements, and ask about alcohol before you drink.

Signs of overdose

A guanfacine overdose can cause very low blood pressure, an unusually slow heart rate, extreme drowsiness, or fainting. If you suspect an overdose, call 911 or Poison Control at 1-800-222-1222 right away.

Safety tips for taking guanfacine

A few everyday habits can help you take guanfacine as safely as possible.

Wait until you know how guanfacine affects you before driving

Guanfacine can make you drowsy or dizzy, so skip driving, operating machinery, or other tasks that need full alertness until you know how it affects you.

Get up slowly from sitting or lying down

To ease the lightheadedness that can come with lower blood pressure, rise slowly when you get up from a chair or bed, especially in the morning.

Keep enough medication on hand

Because missed doses and sudden stops can trigger rebound effects, refill your prescription before you run out and keep a small buffer supply for travel or busy weeks.

Tell every health care provider you take guanfacine

Make sure every provider you see — including dentists, specialists, and pharmacists — knows you take guanfacine so they can account for it in your care.

Check your blood pressure and heart rate regularly

Since guanfacine affects blood pressure and heart rate, your prescriber may ask you to monitor them at home or at regular visits. It can help to keep those check-ins on the calendar.

Guanfacine side effects in children

For children and teens taking Intuniv (guanfacine ER) for ADHD, the side effects look much like they do in adults — most commonly sleepiness, tiredness, trouble sleeping, headache, stomach pain, and irritability. Intuniv side effects tend to be mild, and many get better within the first few weeks.

In those early weeks, keep an eye on how alert your child is during the school day, whether they seem dizzy or unusually tired, and any noticeable shifts in mood or behavior. Rarely, children have experienced changes like agitation or unusual thoughts, so let the prescriber know about anything that seems out of the ordinary. Long-term research following children and teens on guanfacine ER for about two years found that most side effects were mild to moderate, with drowsiness among the most common.

Children and teens usually have regular check-ins with their prescriber to track blood pressure, heart rate, and growth. If a side effect seems to stick around or get worse, reach out to the prescriber rather than adjusting or stopping the medication on your own.

FAQs about guanfacine

Does guanfacine ER cause fewer side effects than guanfacine IR?

The two formulations release the medication differently, so day-to-day experiences can vary from person to person. Your prescriber can explain what to expect from the specific version you're taking.

How should guanfacine be tapered when stopping treatment?

Guanfacine is usually reduced gradually under a prescriber's supervision to avoid rebound effects, rather than stopped all at once. It's best to follow your prescribing provider's plan for coming off the medication.

How long do guanfacine side effects usually last?

Many early side effects, like drowsiness and dizziness, ease within the first few weeks as your body adjusts. If they linger beyond that or feel severe, check in with your prescriber.

Is guanfacine a stimulant medication?

No. Guanfacine is a non-stimulant, which is one reason it's sometimes chosen on its own or added to a stimulant for ADHD.

What should you do if you miss a dose of guanfacine?

Ask your prescriber or pharmacist how to handle a missed dose, and avoid doubling up to catch up. A consistent routine helps you avoid gaps that could bring on rebound effects.

How Headway can help with guanfacine

Medication is only one piece of ADHD care; different talk therapy approaches can help, too.

If you’re looking for a psychiatrist or psychiatric nurse practitioner who can prescribe guanfacine — or help answer your questions about it — Headway can support you. There are thousands of licensed mental health professionals on the Headway network, all of whom take insurance. Use the following directory to find a prescribing provider for medication management, and even a talk therapist for extra support.

This content is for general informational and educational purposes only and does not constitute clinical, legal, financial, or professional advice. All decisions should be made at the discretion of the individual or organization, in consultation with qualified clinical, legal, or other appropriate professionals.

© 2026 Therapymatch, Inc. dba Headway. All rights reserved. No part of this publication may be reproduced without permission.

Medication & prescriptions