7 Guanfacine Side Effects to Keep In Mind - GoodRx (2024)

Guanfacine is a prescription-only alpha agonist medication. Not to be confused with guaifenesin (Mucinex), a similar-sounding cough medicine, guanfacine can manage high blood pressure and symptoms of attention deficit-hyperactivity disorder (ADHD).

It doesn’t just come in one shape or size either. Guanfacine is available in a couple formulations. The immediate-release (IR) tablets are approved to treat high blood pressure in children and adults; the extended-release (ER) tablets (Intuniv) are approved to treat ADHD in kids and adolescents.

These formulations are fairly well-tolerated overall. But, as with all medications, guanfacine can cause side effects. Most are common and go away over time. More serious side effects have been reported, but they’re rare.

Here, we'll talk about seven guanfacine side effects and how to manage them.

1. Drowsiness

Drowsiness is one of the most common guanfacine side effects. It can happen with both guanfacine IR and guanfacine ER. This is especially true when first starting the medication or after raising your dose. The good news is you should feel less drowsy as your body gets used to the medication.

Managing drowsiness

When you’re starting guanfacine or changing your dose, do your best to avoid activities that require alertness, like driving. Once your body gets used to guanfacine, you can decide if engaging in these activities is safe. It's also best to avoid alcohol and other medications that can make you feel drowsy (like opioids, sleep medications, and benzodiazepines).

To help with drowsiness, consider taking guanfacine in the evening. This can help limit the amount of daytime drowsiness you feel.

What’s more, if you’re taking guanfacine ER, you should avoid taking doses with foods high in fat (e.g., fried foods and greasy foods, like pizza). Taking this medication with high-fat foods may raise medication levels too much and cause excessive drowsiness.

2. Dry mouth

In clinical trials, up to 54% of people taking guanfacine IR reported dry mouth. It was less common for guanfacine ER — only about 4% of participants reported it. Regardless of the form, this side effect is more common with higher doses of guanfacine and should improve as your body gets used to the medication.

Symptoms of dry mouth can include persistent thirst and trouble chewing or swallowing food. More than just an annoyance, continued dry mouth can also lead to dental problems.

Managing dry mouth

To help relieve the uncomfortable symptoms of dry mouth, do your best to stay hydrated. This is a good preliminary step to take. Sucking on ice chips, chewing sugar-free gum, or using saliva substitutes may help, too. It's also important to brush and floss your teeth twice daily and continue to see your dentist for regular checkups and cleanings.

Talk to your healthcare provider if your dry mouth continues or becomes a big annoyance. They may consider switching you to a different medication.

3. Dizziness and weakness

Dizziness is another common guanfacine side effect. But it's more common with the IR tablets. In clinical trials, up to 15% of people taking guanfacine IR (and 6% of people using guanfacine ER) felt dizzy at some point. Weakness has also been reported, but less often than dizziness.

Managing dizziness and weakness

If you're feeling dizzy or weak, try to find a safe place to sit or lie down so you don't accidentally fall down and get hurt. Be careful when you're changing positions from sitting to standing, too.

If you experience excessive dizziness or weakness from guanfacine that doesn't improve, let your healthcare provider know. They may lower your dose or switch you to another medication if you frequently feel off balance or weak.

4. Headache

You may develop headaches when you're taking guanfacine. It's possible with both formulations.

But, it's important to remember that headaches could be caused by many different things — not just the medication. Not getting enough sleep and not drinking enough water can trigger headaches, especially in people prone to them. Factors like stress, weather patterns, and other health conditions don’t help either.

Managing headaches

There are a few things you can try at home for headache relief if your headaches become bothersome. Staying hydrated throughout the day and getting enough sleep are good starting points. You can also ask your healthcare provider if it's safe for you to take medications like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin). These short-term medications may offer added pain relief.

5. Constipation and stomach upset

Guanfacine can cause constipation and upset stomach. Of these, constipation is more common. You may notice these guanfacine side effects more when first starting the medication. They should go away with time.

Managing stomach symptoms

Drinking water, exercising, and trying high-fiber foods may help ease constipation. High-fiber foods include fruits, vegetables, and whole grains (e.g., oats and rice). You can also talk to your healthcare provider about trying an over-the-counter (OTC) stool softener or laxative for temporary relief.

If you're experiencing an stomach upset and you take guanfacine IR, try taking your next dose with food to help lessen stomach upset. But remember, guanfacine ER shouldn't be taken with high-fat foods. These foods can affect how your body absorbs guanfacine ER. This may add to more intense side effects.

6. Low blood pressure

Up to 7% of people taking guanfacine ER tablets during clinical trials reported low blood pressure. It doesn’t happen often with the IR tablets.

Low blood pressure can make you feel dizzy or light-headed or cause you to faint. This is more likely to happen when you start taking it or raise your dose. And people with a history of low blood pressure and heart problems may be at a higher risk for this side effect.

Managing low blood pressure

Drops in blood pressure happen more often if you’re taking guanfacine with other blood pressure medications. Sometimes, people need to adjust their dosage of either medication to improve or resolve low blood pressure. But staying well hydrated and moving slowly when you get up from a seated position can help prevent you from falling down or fainting.

Your healthcare provider will likely keep an eye on your blood pressure at your appointments to make sure there aren't any big changes. They may want you to watch your blood pressure at home, too.

7. Sexual difficulties

Erectile dysfunction (ED) can occur with guanfacine, namely the IR version. But like some of the side effects mentioned previously, it's likely to improve over time.

Guanfacine is also only one possible cause of ED. It's important to remember that other things, such high blood pressure, performance anxiety, and older age, can contribute to ED, too.

Managing ED

Let your healthcare provider know if you notice any sexual problems while taking guanfacine. They can help find the underlying cause. In some cases, they may recommend switching to another medication.

Does guanfacine ER have less side effects than guanfacine IR?

Yes. While they share the same active ingredient, clinical studies have shown that guanfacine ER usually has less side effects than guanfacine IR. This is likely because guanfacine ER is slowly absorbed into the bloodstream, allowing the medication to stay at a steady level in the body. This helps lower the risk of side effects.

When should I contact my healthcare provider about guanfacine side effects?

Most guanfacine side effects are mild and improve as your body gets used to the medication. But you should let your healthcare provider know any time you have concerns about side effects that are bothersome or don't go away. They may help you change your dose or your treatment plan altogether.

But, if you notice more serious side effects, including extreme dizziness, severe headache, or long-lasting constipation, call your healthcare provider right away.

You should never stop taking guanfacine ER or IR suddenly. Doing so can cause dangerously high blood pressure and severe headaches. It could also make you feel nervous and shaky. If you have any of these symptoms, get medical help right away.