Key takeaways

Guanfacine, an alpha adrenergic receptor agonist, is used to lower blood pressure in adults and improve attention in children with ADHD, with common side effects varying based on the condition being treated.
Serious side effects of guanfacine can include slowed heart rate, very low blood pressure, hallucinations, and severe allergic reactions, with the potential for long-term or lifelong consequences.
Side effects of guanfacine are dose-dependent and may vary based on the condition being treated, the formulation prescribed (immediate-release for hypertension, extended-release for ADHD), and other concurrent medications.
To avoid or manage guanfacine side effects, patients should give a full medical history, provide a complete list of current medications to their healthcare provider, follow prescription instructions, take the daily dose at night, avoid alcohol, do not take guanfacine with a high-fat meal, and seek medical advice for severe or persistent side effects.

The generic prescription drug guanfacine reduces blood pressure in adults diagnosed with high blood pressure. Brand-name guanfacine, Intuniv, is sometimes prescribed to improve attention in children and teens with attention deficit hyperactivity disorder (ADHD). Healthcare providers at times prescribe guanfacine off-label for other medical conditions.

As an alpha adrenergic receptor agonist, guanfacine is a stimulant. As such, it increases activity in the brain that is responsible for attention and controlling impulsivity in children with ADHD. However, it also reduces the strength of the brain’s nerve impulses to blood vessels, causing them to widen and reducing blood pressure. Different formulations are used for each condition: immediate-release (IR) guanfacine for hypertension and extended-release (ER) guanfacine for ADHD. The types and likelihood of side effects are based on the condition being treated, the formulation prescribed, and other drugs being used for the same condition.

Common side effects of guanfacine

Many common side effects are dose-dependent, that is, they’re more likely to be experienced at higher doses. However, sleepiness is the most common side effect of guanfacine no matter what it’s taken for.

Common side effects of guanfacine (ER) when prescribed for ADHD include:

Sleepiness
Abdominal pain
Fatigue
Decreased appetite
Irritability
Low blood pressure
Dizziness
Lethargy
Nausea
Vomiting
Urinary incontinence
Slow heart rate
Diarrhea
Nightmares
Rash
Weakness
Dry mouth

Common side effects of guanfacine (IR) when prescribed for high blood pressure include:

Dry mouth
Sleepiness
Weakness
Dizziness
Headache
Impotence (at higher doses)
Constipation (at higher doses)
Fatigue

Serious side effects of guanfacine

The most serious side effects of guanfacine include:

Slowed heart rate
Heart block (ER form)
Very low blood pressure (ER form)
Hallucinations (ER form)
Wheezing
Severe allergic reactions
Fainting or passing out
Seizures (ER form)
High blood pressure if stopped suddenly
Withdrawal symptoms if stopped suddenly

Weight gain

Weight gain is an uncommon side effect of guanfacine, occurring primarily in children taking extended-release guanfacine. In clinical trials, approximately 3% of children had a weight increase, but that compares to 2% of participants who gained weight but did not take guanfacine. Weight gain is not a side effect among adults taking guanfacine for high blood pressure. As with any prescription drug, if weight goes up involuntarily, get medical advice from the prescribing healthcare provider.

Mood swings

Mood swings are an uncommon side effect in children and adolescents prescribed guanfacine for ADHD. In at least one clinical trial, about 1% to 3% of children had problems with mood changes, but at least 1% of participants not taking guanfacine also reported mood swings. The incidence does not seem to be related to the size of the daily dose. Mood swings are not a reported side effect of guanfacine in adults. Mood swings can interfere with a child’s daily functioning, so report any mood problems to the prescribing healthcare provider.

Insomnia

Insomnia may occur in children and adults who take guanfacine. In clinical trials for both immediate-release tablets for adults with high blood pressure and extended-release tablets for children with ADHD, about 4% to 8% of participants had a problem with sleeplessness during treatment. Because the most common side effect of guanfacine is sleepiness, problems with insomnia were lowest among participants taking guanfacine in the evening. Report any problems with falling asleep or staying asleep to the prescribing healthcare provider. There are effective ways to manage sleep problems.

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How soon do guanfacine side effects start?

Guanfacine begins to work as a central nervous system stimulant and blood pressure-lowering drug with the first dose, though it may take a few weeks to show improvement in controlling ADHD symptoms. After a dose is taken, immediate-release guanfacine hits its maximum concentration in the body in one to four hours, and five hours for extended-release guanfacine. Many transient side effects such as dry mouth, abdominal pain, headache, nausea, and diarrhea may be experienced during that time. Some other side effects may occur weeks or months after starting treatment.

How long do guanfacine side effects last?

Some of guanfacine’s minor side effects are temporary and get better over time. The remainder usually improves after guanfacine is discontinued. Because it takes the body 17 to 18 hours to clear half a dose of guanfacine, it may take two or three days for side effects to go away after the last dose. Some of the more severe side effects, though rare, may have long-term or lifelong consequences.

What are the long-term side effects of guanfacine?

As both a blood pressure medication and an ADHD medication, guanfacine treatment may last for months or even years. While side effects are common, there are no side effects specifically resulting from long-term use.

Guanfacine contraindications

Guanfacine is never prescribed to anyone with known allergies to the drug.

Pregnancy

Guanfacine is used cautiously during pregnancy. Animal studies suggest there is no risk to the fetus, but there are no studies on humans.

Breastfeeding

Guanfacine is used cautiously in people who are breastfeeding. It is not known if guanfacine is present in human breast milk or if there are risks to the nursing infant. Guanfacine does reduce prolactin, the hormone that’s responsible for lactation. This may affect the ability to produce breast milk while guanfacine is being taken.

Children

Extended-release guanfacine is FDA-approved for children ages 6 to 17 to treat ADHD. Children and teens are more likely than adults to have emotional or psychiatric symptoms with guanfacine. These symptoms include irritability, aggression, mood changes, and—rarely—hallucinations. Guanfacine should be stored securely at room temperature and out of the reach of children.

Seniors

Older adults will be prescribed guanfacine cautiously. There are two reasons. First, older adults are more susceptible to the sedative effects of the drug, raising the risk of falls, accidents, and injuries. Second, older adults clear the drug more slowly from the body, increasing the risk for side effects. Healthcare providers are urged to start seniors at low doses.

Guanfacine warnings

As with every prescription drug, guanfacine is not safe for everyone. It also has potential hazards that people taking the drug should be aware of.

Cautions

Some medical conditions increase the risk of side effects with guanfacine. Greater caution, lower doses, or stricter monitoring may be required. These medical conditions include:

Heart and vascular problems: Because of guanfacine’s effects on the heart, people with cardiovascular disease, coronary artery disease, recent heart attack, slow heartbeat, heart block, or any problems with heart rhythms may require lower doses and closer monitoring.
Liver disease or kidney disease: People with reduced liver or kidney function will clear guanfacine from the body more slowly than usual, increasing the risk for side effects.
Low blood pressure: When guanfacine is prescribed for a condition other than high blood pressure, it can cause low blood pressure. People who already have low blood pressure, are dehydrated, faint easily, or experience a sudden drop in blood pressure when standing (orthostatic hypotension) are particularly at risk.

Abuse and dependence

Guanfacine is not a controlled substance or considered a drug abuse risk.

Guanfacine does, however, cause withdrawal symptoms when abruptly discontinued. Stopping guanfacine suddenly can cause a sudden and steep rise in blood pressure. In some cases, this rebound hypertension will cause mild to serious neurological problems. When either immediate-release or extended-release guanfacine is stopped, doses will be steadily decreased to prevent rebound hypertension and other withdrawal symptoms. Heart rate and blood pressure may need to be monitored as the dose is reduced.

Withdrawal symptoms include headache, confusion, agitation, shaking, and nervousness. The most severe symptoms requiring emergency medical treatment are severe headache, vomiting, vision problems, trouble balancing, excessive sleepiness, or seizures.

Overdose

Call a poison control center or get emergency medical treatment if a guanfacine overdose is suspected. Symptoms of an overdose include drowsiness, low blood pressure, slow heartbeats, and moving around slowly. Coma is also possible . The maximum FDA-approved dose is 4 mg per day. Don’t exceed the prescribed dose for any reason.

Guanfacine interactions

Guanfacine has some hazardous drug interactions. None of these are dangerous enough to prohibit combining guanfacine with another drug, but many require caution. These include:

Other alpha agonists: Alpha agonists like guanfacine and clonidine are used to lower blood pressure or treat ADHD. They all work the same way and have most of the same side effects. Taking more than one alpha agonist could worsen the side effects of both.
Drugs that block the body’s breakdown of guanfacine: Some drugs interfere with the liver’s metabolism of guanfacine, raising the risk of side effects. In some cases, the guanfacine dose may need to be lowered. These drugs include some macrolide antibiotics, azole antifungals, and some HIV/AIDS antiviral medications.
Tricyclic antidepressants: First-generation antidepressants block the ability of guanfacine to lower blood pressure and may significantly contribute to rebound hypertension when guanfacine is discontinued.
Drugs that lower blood pressure: Even though guanfacine is normally prescribed with other blood pressure medications, some combinations can result in blood pressure dropping too low. Other drugs can also lower blood pressure, such as opioids, sleeping aids, and alcohol.
Drugs that raise blood pressure: Some drugs raise blood pressure including stimulant medications, migraine drugs, ADHD medications, over-the-counter decongestants, NSAIDs, and caffeine. While not dangerous, taking these drugs will counteract the therapeutic benefits of taking guanfacine for blood pressure.
Drugs that cause sleepiness: Drugs that cause sedation or drowsiness will worsen the sedative effects of guanfacine. These include sleep aids, antidepressants, benzodiazepines, barbiturates, anxiety medications, opioids, marijuana, alcohol, and over-the-counter drugs like antihistamines.

How to avoid guanfacine side effects

Possible side effects will vary depending on whether guanfacine is being used for hypertension or ADHD. Even so, a few general pointers can help people avoid side effects.

1. Give the prescriber a complete medical history

The most efficient way to avoid side effects is to tell the prescriber about certain medical conditions including:

Low blood pressure
Heart disease
Liver disease
Kidney problems

2. Give the prescriber and pharmacist a complete list of drugs being taken

Many drugs and supplements can interact with guanfacine, so make sure that both the prescriber and pharmacist know about all prescription drugs, over-the-counter medications, and supplements being taken.

3. Take guanfacine as prescribed

Follow all the instructions given by the prescriber and written on the prescription label, as well as the drug information included with guanfacine. If a dose is missed, it can be taken when remembered. But don’t take the missed dose if it’s almost time for the next dose. Just take the next dose when it’s time.

4. Take the daily guanfacine dose at night

To avoid drowsiness and other problems throughout the day, take each day’s dose at night.

5. Don’t take guanfacine tablets with a high-fat meal

Guanfacine tablets can be taken on an empty stomach or with a meal. However, if the tablets are taken with fatty foods, the body will absorb more of the drug, increasing the chances of side effects.

6. Avoid drinking

Drinking alcohol will worsen the sedative effects of guanfacine, so it’s best to either avoid drinking or to drink very little. The same applies to any medicine, supplement, or drug that causes sleepiness and reduces alertness.

How to treat side effects of guanfacine

Sometimes, side effects can’t be avoided. Mild adverse effects can usually be managed. Others, however, will require medical attention.

Sleepiness

If feeling tired or sleepy, sit or lie down to rest. The primary goal is to prevent falling, accidents, or injury. Avoid driving, operating machinery, hazardous activities, or even cutting vegetables. Contact a healthcare professional if severe drowsiness is experienced.

Dry mouth

Sugarless gum or candy can help. Sipping water can, too, but don’t overdo it. If dry mouth is intolerable, ask a healthcare professional about possible treatments such as artificial saliva.

Vomiting

Because of the risk for rebound high blood pressure, immediately talk to a healthcare professional if vomiting or any other condition interferes with the ability to take guanfacine.

Low blood pressure

Low blood pressure is primarily a risk for pediatric patients taking guanfacine for ADHD symptoms. Call a healthcare provider when symptoms of low blood pressure are noticed. These include lightheadedness, dizziness, fainting, trouble concentrating, and tiredness.

Slow heart rate

If heartbeats seem to be slow, immediately talk to a healthcare professional.

Sources

Guanfacine, Epocrates
Guanfacine, Drugs and Lactation Database
Guanfacine drug summary, Prescriber’s Digital Reference
Guanfacine hydrochloride extended-release tablet prescribing information, U.S. National Library of Medicine
Guanfacine hydrochloride tablet prescribing information, U.S. National Library of Medicine
Guanfacine (Intuniv), National Alliance on Mental Illness