Guanfacine Side Effects

As of March 31, 2024, the most commonly reported guanfacine side effects include drowsiness, aggression, low blood pressure, slow heart rate and dizziness, according to the Food and Drug Administration’s Adverse Events Reporting System.

Severe side effects include slow heart rate, severe hypotension (low blood pressure) and fainting. In rare cases, guanfacine can cause severe allergic reactions, including rash, itching and swelling of the face, tongue or throat. This can cause difficulties in breathing.

About 60% of all reported side effects were serious, with 6.7% of the reports claiming that the drug caused death. The number of reports have climbed significantly within the last few years, with about 44% of all reports being from 2021 and later.

The most common guanfacine side effects reported during clinical trials include drowsiness and fatigue. These had the biggest impact on study discontinuation. Side effects were more pronounced with higher doses of guanfacine.

Abrupt discontinuation of the drug can also result in withdrawal symptoms such as nervousness, agitation, headache and a rapid increase in blood pressure. Therefore, patients should follow the guidance of their health care providers to avoid these adverse effects​.

How Long Do Guanfacine Side Effects Last?

Most mild effects go away within a day, but some can take 48-72 hours to wear off.

Although mild guanfacine side effects usually go away on their own, they can affect daily tasks that require alertness and concentration. For instance, drowsiness and fatigue may affect school performance in children using guanfacine for ADHD and hinder adults from operating machinery safely.

Severe adverse effects, though rare, may take weeks to resolve or even last a lifetime. The length it takes for guanfacine side effects to wear off depends on the dosage, patient’s metabolism and physiology.

Guanfacine can cause serious cardiovascular and psychological side effects. Though rare, pediatric patients are more likely to report hallucinations. Additionally, allergic reactions can become life-threatening.

The risk of side effects increases when overdosing. A 2024 study in the International Journal of Emergency Medicine highlights the risks of cardiovascular events associated with guanfacine toxicity.

Guanfacine and Hypotension

Guanfacine can trigger drops in blood pressure, which can lead to dizziness, fainting and falls. Patients who have a predisposition to low blood pressure or are taking blood pressure-lowering medications are at a particularly high risk. Monitoring blood pressure regularly and adjusting the dose as necessary can help manage this risk.

When To Seek Medical Attention

If you experience severe dizziness, fainting, irregular heartbeats, severe abdominal pain, depression, hallucinations or severe allergies such as rash, itchiness, swelling, dizziness or shortness of breath, seek immediate medical attention.

These symptoms can become life-threatening if untreated, but prompt medical intervention can help prevent severe reactions from becoming fatal.

Prescribing information includes warnings for hypotension, slow heart rate, sedation and somnolence (sleepiness), syncope (loss of consciousness) and cardiac conduction abnormalities.

There is also a warning for the possibility of rebound hypertension, which is a sudden increase in blood pressure when the medication stops. It can lead to brain dysfunction known as hypertensive encephalopathy. Careful withdrawal from guanfacine under a physician’s guidance can help minimize the risk of developing rebound hypertension.

Methods to manage Guanfacine side effects include following your doctor’s instructions, staying hydrated, avoiding alcohol, taking appropriate doses and reporting adverse reactions to your doctor as soon as possible.

Before taking guanfacine, speak with your prescribing physician about any known allergies to lessen the risk of a hypersensitive reaction. Even if you have no guanfacine allergy, you may be allergic to other ingredients in the medication.

Suitable guanfacine alternatives depend on if the medication is being used to treat high blood pressure or ADHD.

Some alternative medications used to control high blood pressure include angiotensin converting enzyme (ACE) inhibitors and alpha-2 adrenergic agonists.

Alternative medications for ADHD treatment include adrenergic reuptake inhibitors and prescribed stimulants.

Alternatives for High Blood Pressure

ACE Inhibitors

ACE inhibitors, such as lisinopril, work by preventing blood vessels from constricting, which can decrease blood pressure. This class of medicine comes with a black box warning for fetal harm if taken while pregnant. This drug may also be dangerous for patients with kidney problems.

Clonidine

Like guanfacine, clonidine is an alpha-2 adrenergic agonist used to treat conditions such as ADHD and low blood pressure. These types of medicine help calm the sympathetic nervous system and reduce adrenaline.

While similar, clonidine and guanfacine differ in regard to which specific alpha-2 receptors they interact with. The best choice could depend on your brain chemistry.

Alternatives for ADHD

Atomoxetine (Straterra)

This is a non-stimulant adrenergic reuptake inhibitor. This drug class increases levels of norepinephrine, which is a chemical that aids in focus.

The black box warning for atomoxetine includes increased risk of depression and suicidal ideation. However, it has less side effects than guanfacine overall and has no adverse interaction with alcohol.

Stimulant Medications

Doctors commonly prescribe drugs such as methylphenidate (Ritalin) or amphetamine salts (Adderall) for ADHD. Both Ritalin and Adderall are fast-acting compared to guanfacine. However, these medications may increase the risk of heart problems, so those with high blood pressure should be especially cautious.

Like all prescription stimulants, methylphenidate and amphetamine salts have a black box warning for potential addiction. They may also exacerbate anxiety.

Patients on stimulants and patients on guanfacine should avoid consuming alcohol. Unlike guanfacine, however, stimulants rarely cause drowsiness.

Discuss your concerns about side effects with your health care provider so they can help you find a suitable replacement. Factors such as your other medications, pre-existing conditions and treatment goals will determine what treatments are safe and effective for you.

Editor Lindsay Donaldson contributed to this article.