From the Guidelines
Clonidine can cause several side effects, including drowsiness, dizziness, fatigue, dry mouth, constipation, and headache, and more serious side effects such as severe low blood pressure, fainting, slow heart rate, depression, and allergic reactions, and should be tapered gradually under medical supervision to avoid rebound hypertension. The medication works by stimulating alpha-2 adrenergic receptors in the brain, which reduces sympathetic outflow and lowers blood pressure, explaining why drowsiness and dry mouth are common side effects 1. Common side effects of clonidine include:
- Drowsiness
- Dizziness
- Fatigue
- Dry mouth
- Constipation
- Headache More serious side effects that require medical attention include:
- Severe low blood pressure
- Fainting
- Slow heart rate
- Depression
- Allergic reactions Patients taking clonidine should avoid alcohol and be cautious when driving or operating machinery due to the sedative effects, and it's essential to take clonidine exactly as prescribed and report any concerning side effects to your healthcare provider promptly 1. It's also important to note that clonidine can cause rebound hypertension if stopped suddenly, so it should always be tapered gradually under medical supervision 1. In addition, clonidine may precipitate or exacerbate depression, bradycardia, and orthostatic hypotension, and sudden cessation of treatment can produce a withdrawal syndrome 1. Overall, clonidine is generally reserved as a last-line treatment due to its significant CNS adverse effects, especially in older adults 1.
From the FDA Drug Label
In patients who have developed localized contact sensitization to clonidine transdermal system, continuation of clonidine transdermal system or substitution of oral clonidine hydrochloride therapy may be associated with the development of a generalized skin rash In patients who develop an allergic reaction to clonidine transdermal system, substitution of oral clonidine hydrochloride may also elicit an allergic reaction (including generalized rash, urticaria, or angioedema). The sympatholytic action of clonidine may worsen sinus node dysfunction and atrioventricular (AV) block, especially in patients taking other sympatholytic drugs There are post-marketing reports of patients with conduction abnormalities and/or taking other sympatholytic drugs who developed severe bradycardia requiring IV atropine, IV isoproterenol and temporary cardiac pacing while taking clonidine. Patients should be cautioned against interruption of clonidine hydrochloride tablets therapy without their physician's advice. Since patients may experience a possible sedative effect, dizziness, or accommodation disorder with use of clonidine, caution patients about engaging in activities such as driving a vehicle or operating appliances or machinery Also, inform patients that this sedative effect may be increased by concomitant use of alcohol, barbiturates, or other sedating drugs. Patients who wear contact lenses should be cautioned that treatment with clonidine hydrochloride tablets may cause 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 (QT-prolongation, ventricular fibrillation) of high intravenous doses of haloperidol. In several studies with oral clonidine hydrochloride, a dose-dependent increase in the incidence and severity of spontaneous retinal degeneration was seen in albino rats treated for six months or longer. Tissue distribution studies in dogs and monkeys showed a concentration of clonidine in the choroid In view of the retinal degeneration seen in rats, eye examinations were performed during clinical trials in 908 patients before, and periodically after, the start of clonidine therapy. In 353 of these 908 patients, the eye examinations were carried out over periods of 24 months or longer Except for some dryness of the eyes, no drug-related abnormal ophthalmological findings were recorded and, according to specialized tests such as electroretinography and macular dazzle, retinal function was unchanged. In combination with amitriptyline, clonidine hydrochloride administration led to the development of corneal lesions in rats within 5 days Hypertension may develop early and may be followed by hypotension, bradycardia, respiratory depression, hypothermia, drowsiness, decreased or absent reflexes, weakness, irritability and miosis. The frequency of CNS depression may be higher in children than adults. Large overdoses may result in reversible cardiac conduction defects or dysrhythmias, apnea, coma and seizures Signs and symptoms of overdose generally occur within 30 minutes to two hours after exposure. As little as 0. 1 mg of clonidine has produced signs of toxicity in children.
The side effects of clonidine include:
- Generalized skin rash
- Allergic reactions (including urticaria or angioedema)
- Worsening of sinus node dysfunction and atrioventricular (AV) block
- Severe bradycardia
- Sedative effect
- Dizziness
- Accommodation disorder
- Dryness of eyes
- CNS-depressive effects
- Orthostatic regulation disturbances (e.g., orthostatic hypotension, dizziness, fatigue)
- Sinus bradycardia
- Corneal lesions
- Spontaneous retinal degeneration
- Hypertension
- Hypotension
- Bradycardia
- Respiratory depression
- Hypothermia
- Drowsiness
- Decreased or absent reflexes
- Weakness
- Irritability
- Miosis
- Reversible cardiac conduction defects or dysrhythmias
- Apnea
- Coma
- Seizures 2 2
From the Research
Clonidine Side Effects
- The side effects of clonidine include somnolence, fatigue, headache, bradycardia, hypotension, and clinically insignificant electrocardiographic changes 3
- Clonidine has also been reported to cause dry mouth and sedation, particularly at high doses 4
- In some cases, clonidine has been associated with serious cardiac side effects, including death, although these are typically seen in patients with other risk factors 3
- Common side effects of clonidine in the treatment of attention-deficit hyperactivity disorder (ADHD) include somnolence, fatigue, and headache 3
- Clonidine has also been used to treat other conditions, such as post-traumatic stress disorder (PTSD) and obsessive-compulsive disorder (OCD), although the evidence for its use in these conditions is limited 5, 6
Cardiovascular Safety
- Clonidine has been shown to have a favorable cardiovascular safety profile compared to other medications used to treat ADHD, such as amphetamines and methylphenidate 7
- Clonidine has been associated with decrements in haemodynamic values, including systolic blood pressure, diastolic blood pressure, and pulse, in both children and adults 7
- However, the long-term effects of clonidine on cardiovascular parameters are not well understood and require further study 7