Side Effects of Catapres (clonidine)

Catapres (clonidine) is a centrally acting alpha-agonist hypotensive agent used to treat high blood pressure (hypertension). It may be used alone or combined with other drugs used for the treatment of high blood pressure.

Catapres is also used off-label to treat alcohol withdrawal, smoking cessation (nicotine withdrawal), restless leg syndrome, Tourette’s syndrome, opioid withdrawal, diabetes-associated diarrhea, diabetic neuropathy (nerve damage), hot flashes associated with menopause, and smoking cessation. It also can be used as an adjunct to manage severe cancer-related pain.

It acts by stimulating receptors on nerves in the brain that reduces the transmission of messages from nerves in the brain to nerves in other areas of the body. As a result, it slows the heart rate and reduces blood pressure.

Common side effects of Catapres include

• tiredness,
• lethargy,
• fatigue,
• drowsiness,
• weakness,
• constipation,
• dry mouth,
• headache,
• dizziness,
• skin redness,
• itching,
• darkening of skin,
• impotence,
• decreased sexual desire, and
• ejaculatory dysfunction.

Serious side effects of Catapres include

• severe rebound high blood pressure (more likely to occur if Catapres is stopped suddenly; symptoms of severe rebound high blood pressure can include increased salivation, nervousness, headache, heart palpitations, agitation, anxiety, sweating, nausea, muscle pain, and abdominal pain),
• severe low blood pressure,
• slow heart rate,
• withdrawal symptoms,
• depression,
• angioedema,
• severe allergic reactions,
• fainting, and
• abnormal heart conduction.

Drug interactions of Catapres include other medications that cause sedation such as narcotic pain relievers, barbiturates, sedatives such as alprazolam and clonazepam, and ethanol because Catapres can increase the sedating effects of these drugs.

• Tricyclic antidepressants can block the blood pressure lowering effects of Catapres. This may cause blood pressure to rise. Since Catapres can reduce heart rate, it should be used cautiously in persons who are receiving any other medication that lowers heart rate such as beta-blockers.
• Abnormal heart rhythms can occur with a combination of Catapres and verapamil.
• Cyclosporine concentrations in the blood can increase when Catapres is begun. This interaction could result in kidney damage from the increased levels of cyclosporine.
• Nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce the antihypertensive effects of Catapres. Cocaine, pseudoephedrine, phenylephrine, and phenylpropanolamine also can reverse the blood pressure lowering effects of Catapres.

There are no adequate studies of Catapres use during pregnancy. Catapres is excreted into breast milk and potentially could cause adverse effects in the infant. Consult your doctor before breastfeeding. 

The most common side effects are:

• Tiredness
• Lethargy
• Drowsiness
• Constipation
• Dry mouth
• Headache
• Dizziness
• Fatigue
• Weakness

Other side effects include:

• Skin redness
• Itching
• Impotence
• Darkening of skin
• Decreased sexual desire
• Ejaculatory dysfunction

Possible serious side effects include:

• Severe rebound high blood pressure
• Severe low blood pressure
• Slow heart rate
• Withdrawal symptoms
• Depression
• Angioedema
• Severe allergic reactions
• Slow heart rate
• Fainting
• Abnormal heart conduction

Severe rebound hypertension can occur following withdrawal from clonidine. This reaction is more likely to occur if clonidine is stopped suddenly (without a gradual dose reduction).

Symptoms of severe rebound high blood pressure can include:

• Increased salivation
• Nervousness
• Headache
• Heart palpitations
• Agitation
• Anxiety
• Sweating
• Nausea
• Muscle pain
• Abdominal pain

Slowly reducing the dose of this medication over several days will prevent these symptoms.

Most adverse effects are mild and tend to diminish with continued therapy. The most frequent (which appear to be dose-related) are dry mouth, occurring in about 40 of 100 patients; drowsiness, about 33 in 100; dizziness, about 16 in 100; constipation and sedation, each about 10 in 100.

The following less frequent adverse experiences have also been reported in patients receiving Catapres tablets, but in many cases patients were receiving concomitant medication and a causal relationship has not been established.

• Body as a Whole: Fatigue, fever, headache, pallor, weakness, and withdrawal syndrome. Also reported were a weakly positive Coombs' test and increased sensitivity to alcohol.
• Cardiovascular: Bradycardia, congestive heart failure, electrocardiographic abnormalities (i.e., sinus node arrest, junctional bradycardia, high degree AV block and arrhythmias), orthostatic symptoms, palpitations, Raynaud's phenomenon, syncope, and tachycardia. Cases of sinus bradycardia and atrioventricular block have been reported, both with and without the use of concomitant digitalis.
• Central Nervous System: Agitation, anxiety, delirium, delusional perception, hallucinations (including visual and auditory), insomnia, mental depression, nervousness, other behavioral changes, paresthesia, restlessness, sleep disorder, and vivid dreams or nightmares.
• Dermatological: Alopecia, angioneurotic edema, hives, pruritus, rash, and urticaria.
• Gastrointestinal: Abdominal pain, anorexia, constipation, hepatitis, malaise, mild transient abnormalities in liver function tests, nausea, parotitis, pseudo-obstruction (including colonic pseudo-obstruction), salivary gland pain, and vomiting.
• Genitourinary: Decreased sexual activity, difficulty in micturition, erectile dysfunction, loss of libido, nocturia, and urinary retention.
• Hematologic: Thrombocytopenia.
• Metabolic: Gynecomastia, transient elevation of blood glucose or serum creatine phosphokinase, and weight gain.
• Musculoskeletal: Leg cramps and muscle or joint pain.
• Oro-otolaryngeal: Dryness of the nasal mucosa.
• Ophthalmological: Accommodation disorder, blurred vision, burning of the eyes, decreased lacrimation, and dryness of eyes.

• Clonidine may potentiate the CNS-depressive effects of alcohol, barbiturates or other sedating drugs.
• If a patient receiving clonidine hydrochloride is also taking tricyclic antidepressants, the hypotensive effect of clonidine may be reduced, necessitating an increase in the clonidine dose.
• If a patient receiving clonidine is also taking neuroleptics, orthostatic regulation disturbances (e.g., orthostatic hypotension, dizziness, fatigue) may be induced or exacerbated.
• Monitor heart rate in patients receiving clonidine concomitantly with agents known to affect sinus node function or AV nodal conduction, e.g., digitalis, calcium channel blockers and beta-blockers.
• Sinus bradycardia resulting in hospitalization and pacemaker insertion has been reported in association with the use of clonidine concomitantly with diltiazem or verapamil.
• Amitriptyline in combination with clonidine enhances the manifestation of corneal lesions in rats.
• Based on observations in patients in a state of alcoholic delirium it has been suggested that high intravenous doses of clonidine may increase the arrhythmogenic potential (QTprolongation, ventricular fibrillation) of high intravenous doses of haloperidol.
• Causal relationship and relevance for clonidine oral tablets have not been established.