Guanfacine belongs to the class of medications called alpha adrenergic agonists. It is used alone and with stimulant medications to treat symptoms of attention-deficit/hyperactivity disorder (ADHD) in children between the ages of 6 and 17 years. It should be used in combination with other, non-drug measures such as counselling to treat the symptoms of ADHD. Guanfacine is different from other medications used to treat ADHD, because it is not a stimulant medication like methylphenidate or dextroamphetamine. The way that guanfacine works to treat the symptoms of ADHD has not yet been determined.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended starting dose for guanfacine is 1 mg taken once daily. Your child's doctor may gradually increase the dose, based on the effectiveness and side effects of the medication. The maximum daily dose for children 6 to 12 years of age is 4 mg, taken once a day. For adolescents 13 to 17 years of age, the maximum daily dose is 7 mg when used alone or 4 mg when used in combination with another medication for ADHD.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

This medication should be swallowed whole with a small amount of liquid. Do not chew or crush the tablet as this will cause the medication to be absorbed into the body all at once, possibly causing more side effects.

Avoid taking this medication along with a meal that is high in fat.

It is important that this medication be taken exactly as prescribed by your doctor. If this medication is stopped suddenly, both blood pressure and heart rate can increase. If you feel the need to stop the medication, it should be done gradually under supervision of your doctor.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice. If more than 2 doses in a row are missed, contact your doctor for instructions, since you may need to restart at a lower dose.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

1 mg
Each white, round, biconvex tablet debossed with ‘GNF’ on one side and ‘1MG’ on other side, contains guanfacine hydrochloride equivalent to 1 mg of guanfacine. Nonmedicinal ingredients: Colloidal silicon dioxide, crospovidone, eudragit, glyceryl dibehenate, hydroxypropyl methylcellulose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol, and povidone.

2 mg
Each white, oval, biconvex tablet debossed with ‘GNF’ on one side and ‘2MG’ on other side, contains guanfacine hydrochloride equivalent to 2 mg of guanfacine. Nonmedicinal ingredients: Colloidal silicon dioxide, crospovidone, eudragit, glyceryl dibehenate, hydroxypropyl methylcellulose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol, and povidone.

3 mg
Each green, round, biconvex tablet debossed with ‘GNF’ on one side and ‘3MG’ on other side, contains guanfacine hydrochloride equivalent to 3 mg of guanfacine. Nonmedicinal ingredients: colloidal silicon dioxide, crospovidone, eudragit, FD&C Blue No. 2 Aluminum Lake, iron oxide yellow, glyceryl dibehenate, hydroxypropyl methylcellulose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol, and povidone.

4 mg
Each green, oval, biconvex tablet debossed with ‘GNF’ on one side and ‘4MG’ on other side, contains guanfacine hydrochloride equivalent to 4 mg of guanfacine. Nonmedicinal ingredients: colloidal silicon dioxide, crospovidone, eudragit, FD&C Blue No. 2 Aluminum Lake, iron oxide yellow, glyceryl dibehenate, hydroxypropyl methylcellulose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol, and povidone.

Do not give this medication to your child if they are allergic to guanfacine or any ingredients of the medication.

This medication is not intended to be used by children less than 6 years old or adults over the age of 17 years.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• constipation
• decreased appetite
• dizziness
• drowsiness
• dry mouth
• headache
• nausea
• trouble sleeping

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• aggressive or hostile behavior
• dizziness when rising from a sitting or lying position
• fainting
• hallucinations (seeing or hearing things that aren't there)
• low blood pressure
• low heart rate
• psychotic or manic symptoms (e.g., paranoia, delusions, unusual excitement, overactivity)
• sleepiness
• stomach pain

Stop taking the medication and seek immediate medical attention if any of the following occur:

• seizures
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of high blood pressure after suddenly stopping the medication (e.g., agitation, confusion, headaches, nervousness, tremors)
• thoughts of self-harm or suicide

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there other precautions or warnings for this medication

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Abnormal heart rhythms: Guanfacine can cause abnormal heart rhythms. Certain medications (e.g., sotalol, chlorpromazine, pimozide, moxifloxacin, mefloquine, pentamidine, tacrolimus) can increase the risk of a type of abnormal heart rhythm called QT prolongation, and should not be used in combination with this medication. If you have been told that your child is at an increased risk of developing an abnormal heart rhythm, discuss with your doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Blood pressure and heart rate: This medication may cause decreases in blood pressure or heart rate. If you have low blood pressure or are just starting to take this medication, you should move slowly when you are rising from a sitting or lying down position to reduce the risk of dizziness.

Drowsiness and reduced alertness: Guanfacine may affect the mental or physical abilities needed to perform tasks that require special attention. Have your child avoid riding a bike, operating machinery, or performing other hazardous tasks until you have determined how this medication affects your child.

Kidney function: Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If your child has reduced kidney function or kidney disease, discuss with your doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If your child has liver problems, discuss with their doctor how this medication may affect their medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Psychiatric and behavioural concerns: Medications used to treat ADHD, including guanfacine, may increase symptoms of mental illnesses such as bipolar disorder, psychosis, or depression. This medication may cause people to feel agitated (restless, anxious, aggressive, emotional) and not like themselves. If you experience these side effects or notice them in a family member who is taking this medication, contact your doctor immediately. Your child should be closely monitored by your doctor for emotional and behaviour changes while taking this medication.

Self-harm and suicide risk: People with ADHD may have a slightly increased risk of suicidal thoughts and behaviours. Like other medications for ADHD, guanfacine may contribute to this risk. It is important to watch for suicidal thoughts and behaviors and encourage your child to report any worrisome thoughts or feelings to you. Report any concerns to your child's doctor immediately.

Stopping the medication: If this medication needs to be stopped, it should be done gradually, under the supervision of your doctor. Suddenly stopping guanfacine can cause increased blood pressure and heart rate, which, although rare, can cause serious complications, including swelling in the brain. Your doctor can advise you on how to reduce the medication slowly to reduce the risk of developing high blood pressure. If your child complains of headaches or seems confused, nervous, agitated, or has tremors, contact your child's doctor immediately.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if guanfacine passes into breast milk. If you are a breast-feeding and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children less than 6 years old or weighing less than 25 kg. The effectiveness of using this medication to treat ADHD has not been established for adolescents more than 17 years old.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Abnormal heart rhythms: Guanfacine can cause abnormal heart rhythms. Certain medications (e.g., sotalol, chlorpromazine, pimozide, moxifloxacin, mefloquine, pentamidine, tacrolimus) can increase the risk of a type of abnormal heart rhythm called QT prolongation, and should not be used in combination with this medication. If you have been told that your child is at an increased risk of developing an abnormal heart rhythm, discuss with your doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Blood pressure and heart rate: This medication may cause decreases in blood pressure or heart rate. If you have low blood pressure or are just starting to take this medication, you should move slowly when you are rising from a sitting or lying down position to reduce the risk of dizziness.

Drowsiness and reduced alertness: Guanfacine may affect the mental or physical abilities needed to perform tasks that require special attention. Have your child avoid riding a bike, operating machinery, or performing other hazardous tasks until you have determined how this medication affects your child.

Kidney function: Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If your child has reduced kidney function or kidney disease, discuss with your doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If your child has liver problems, discuss with their doctor how this medication may affect their medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Psychiatric and behavioural concerns: Medications used to treat ADHD, including guanfacine, may increase symptoms of mental illnesses such as bipolar disorder, psychosis, or depression. This medication may cause people to feel agitated (restless, anxious, aggressive, emotional) and not like themselves. If you experience these side effects or notice them in a family member who is taking this medication, contact your doctor immediately. Your child should be closely monitored by your doctor for emotional and behaviour changes while taking this medication.

Self-harm and suicide risk: People with ADHD may have a slightly increased risk of suicidal thoughts and behaviours. Like other medications for ADHD, guanfacine may contribute to this risk. It is important to watch for suicidal thoughts and behaviors and encourage your child to report any worrisome thoughts or feelings to you. Report any concerns to your child's doctor immediately.

Stopping the medication: If this medication needs to be stopped, it should be done gradually, under the supervision of your doctor. Suddenly stopping guanfacine can cause increased blood pressure and heart rate, which, although rare, can cause serious complications, including swelling in the brain. Your doctor can advise you on how to reduce the medication slowly to reduce the risk of developing high blood pressure. If your child complains of headaches or seems confused, nervous, agitated, or has tremors, contact your child's doctor immediately.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if guanfacine passes into breast milk. If you are a breast-feeding and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children less than 6 years old or weighing less than 25 kg. The effectiveness of using this medication to treat ADHD has not been established for adolescents more than 17 years old.

There may be an interaction between guanfacine and any of the following:

• acetylcholinesterase inhibitors (e.g., donepezil, galantamine, rivastigmine)
• alcohol
• aldesleukin
• alpha-blockers (e.g., alfuzosin, tamsulosin)
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• antiarrythmics (e.g., amiodarone, dronedarone, flecainide, propafenone)
• antihistamines (e.g., azelastine, cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine, rupatadine)
• antipsychotics (e.g., cariprazine, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• apalutamide
• apomorphine
• aprepitant
• "azole" antifungal agents (e.g., itraconazole, ketoconazole, voriconazole)
• barbiturates (e.g., butalbital, phenobarbital)
• benzodiazepines (e.g., alprazolam, diazepam, lorazepam)
• beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
• bosentan
• brimonidine
• bromocriptine
• buprenorphine
• butorphanol
• calcium channel blockers (e.g., diltiazem, verapamil)
• cannabis
• chloral hydrate
• clonidine
• cobicistat
• diazoxide
• digoxin
• dimenhydrinate
• diphenoxylate
• diuretics (water pills; e.g., bumetanide, furosemide)
• dronedarone
• elagolix
• entacapone
• enzalutamide
• esketamine
• flecainide
• flibanserin
• flunarizine
• general anesthetics (medications used to put people to sleep before surgery)
• grapefruit juice
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine)
• HIV protease inhibitors (e.g., atazanavir, darunavir, lopinavir, ritonavir)
• ivabradine
• kava kava
• ketotifen
• lemborexant
• letermovir
• levodopa
• lumacaftor and ivacaftor
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• methadone
• methylphenidate
• metoclopramide
• midodrine
• mifepristone
• minocycline
• mirtazapine
• mitotane
• modafinil
• monoamine oxidase inhibitors (MAOIs; e.g., phenelzine, rasagiline, selegiline, tranylcypromine)
• muscle relaxants (e.g., baclofen, cyclobenzaprine, methocarbamol, orphenadrine)
• nabilone
• narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone, tapentadol, tramadol)
• nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• nirmatrelvir
• obinutuzumab
• ondansetron
• pentoxifylline
• phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pizotifen
• pomalidomide
• pramipexole
• pregabalin
• quinolone antibiotics (e.g., ciprofloxacin, moxifloxacin, norfloxacin)
• rifabutin
• rifampin
• riociguat
• ropinirole
• rotigotine
• sacubitril
• scopolamine
• St. John's wort
• seizure medications (e.g., carbamazepine, clobazam, levetiracetam, phenobarbital, phenytoin, primidone, rufinamide, topiramate, valproic acid)
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
• serotonin-norepinephrine reuptake inhibitors (e.g., desvenlafaxine, duloxetine, venlafaxine)
• sodium oxybate (GHB)
• somatostatin analogues (e.g., lanreotide, octreotide, pasireotide)
• sphingosine 1-phosphate (S1P) receptor inhibitors (e.g., fingolimod, ponesimod, siponimod)
• tetrabenazine
• thalidomide
• tizanidine
• tofacitinib
• trazodone
• tretinoin
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• tyrosine kinase inhibitors (e.g., ceritinib, crizotinib, dabrafenib, imatinib)
• yohimbine
• zolpidem
• zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.