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Alpha-2 adrenergic agonist

Clonidine

also Clonidine hydrochloride · Catapres · Kapvay

Clonidine is a central alpha-2 adrenergic agonist that lowers sympathetic activity and blood pressure. Its extended-release tablets are also used for ADHD, alone or alongside a stimulant. [1] Pediatric trials support symptom improvement, with sedation, fatigue and slower heart rate as important tradeoffs. [2][3]

An evidence-based non-stimulant option for pediatric ADHD, with sedation and blood-pressure effects that need monitoring.

2D chemical structure of Clonidine
C9H9Cl2N3230.09 g/molCID 2803 ↗
Established5 papers · 2011–2020 · 5 journals · 3 in humans
  • meta-analysis
  • RCT
  • trial
  • observational
  • preclinical / case
  • review / patent / other
  • retracted
2011 · RCT · Clonidine extended-release tablets for pediatric patients with attention-deficit/hyperactivity disorder.2011 · RCT · Clonidine extended-release tablets as add-on therapy to psychostimulants in children and adolescents with ADHD.2011 · review · Safety and efficacy of clonidine and clonidine extended-release in the treatment of children and adolescents with attention deficit and hyperactivity disorders.2018 · meta-analysis · Comparative efficacy and tolerability of medications for attention-deficit hyperactivity disorder in children, adolescents, and adults: a systematic review and network meta-analysis.2020 · other · CLONIDINE HYDROCHLORIDE extended-release tablets, for oral use Initial U.S. Approval: 1974
in its favour
  • + Pediatric ADHD evidence as monotherapy and add-on treatment
  • + A non-stimulant mechanism
watch for
  • − Sleepiness, fatigue and low blood pressure
  • − Abrupt withdrawal can cause rebound hypertension

Overview

Clonidine combines an antihypertensive action with a non-stimulant ADHD indication. The evidence on this page concerns the oral extended-release ADHD formulation; it should not be transferred directly to immediate-release tablets or patches. [1]

In a 236-participant randomized trial, both 0.2 and 0.4 mg/day improved pediatric ADHD ratings versus placebo at week 5. A separate 198-participant trial found additional symptom improvement when extended-release clonidine was added to a stimulant that had provided only a partial response. [2][3]

Results are not uniformly positive across every setting or test. A review found no improvement on a go/no-go performance task in one small trial; in another trial parents reported benefit while teachers did not. The 2018 network meta-analysis identified no qualifying adult clonidine ADHD trials. [4][5]

Mechanism

Clonidine stimulates alpha-2 adrenergic receptors. In the brainstem this reduces sympathetic outflow, lowering peripheral vascular resistance, blood pressure and heart rate. It is not a stimulant, and the exact mechanism responsible for improvement in ADHD is not established. [1]

Direct targetswhat the molecule itself binds or acts on
  • Alpha-2 adrenergic receptorsactivates
    Reduces central sympathetic outflow; the precise mechanism of ADHD benefit remains uncertain. [1]
    strong

Formulation

how the form changes blood levels

Extended release produces a later, lower peak than immediate release. The prescribing information advises against direct milligram-for-milligram substitution, and the extended-release tablets must not be crushed, chewed or broken. [1]

Dosing

as studied or commonly reported; not a recommendation

Doses below are what studies used or, where marked, what is commonly reported. None is a recommendation.

Oral

  • 0.2 or 0.4 mg/day (extended release, after titration)
    236 children and adolescents aged 6–17 with ADHD; monotherapy
    divided morning and bedtime doses · 8-week trial; primary endpoint at week 5
    human study[1][2]
  • 0.1–0.4 mg/day (extended release, titrated)
    198 children and adolescents with ADHD and an incomplete response to methylphenidate or amphetamine
    bedtime initially; higher daily doses split morning and bedtime · 8-week trial; primary endpoint at week 5
    human study[1][3]
Form
Oral clonidine hydrochloride; immediate- and extended-release products are not interchangeable milligram for milligram. Identity fields describe clonidine itself, not its hydrochloride salt. [1]
Time to effect
In the monotherapy trial, rating-scale improvement separated from placebo by week 2. [2]
Notes
These rows report pediatric trial regimens, not adult dosing advice. Extended-release tablets are swallowed whole. Abrupt discontinuation can cause rebound hypertension; the label specifies a supervised taper rather than sudden stopping. [1]

Pharmacokinetics

what the body does with it
Half-lifeAbout 12–16 hours after oral immediate-release clonidine; severe renal impairment can prolong this to approximately 41 hours. [1]
Time to peakIn the label’s single-dose 0.1 mg adult crossover study, mean peak time was about 2.1 hours for immediate release and 6.5 hours for fasted extended release. [1]
Peak levelIn that 0.1 mg study, mean peak concentrations were 443 pg/mL for immediate release versus 258 pg/mL for fasted extended release. [1]
BioavailabilityExtended-release systemic exposure was approximately 89% of immediate release in the adult comparison; this is relative, not absolute, bioavailability. [1]
MetabolismAbout half of the absorbed immediate-release dose is metabolized in the liver. [1]
ExcretionAbout 40–60% of the absorbed immediate-release dose is recovered unchanged in urine within 24 hours. [1]

Safety

risks and cautions, not medical advice

Somnolence, fatigue, hypotension and bradycardia are the central tolerability issues. Historical reports of serious cardiac events had substantial confounding, and the reviewed trials did not establish a causal fatal interaction with methylphenidate. They also cannot exclude rare harms. [4]

Blood pressure and pulse require monitoring, particularly during titration and in people with conduction disease or renal impairment. Sudden withdrawal can cause rebound hypertension. [1]

Adverse effects
reported, not universal
  • Somnolence, fatigue, dizziness, low blood pressure and bradycardia. [4]
Cautions
who should think twice
  • Do not stop suddenly; withdrawal may cause rebound hypertension. [1]
  • Renal impairment and cardiac conduction disease change the monitoring and titration requirements. [1]
Limits of the evidence
what has not been shown
  • Adult ADHD efficacy cannot be inferred from pediatric trials; none qualified for the 2018 network meta-analysis. [5]
  • The reviewed studies did not directly establish that extended-release clonidine is more effective or safer than immediate release. [4]

Interactions

documented pairs only, not exhaustive

Clonidine plus a stimulant is a studied treatment strategy for partial response, not a way to cancel out stimulant adverse effects. [3] Alcohol and other central nervous system depressants can worsen sedation. Antihypertensives can intensify hypotension, while beta blockers, some calcium-channel blockers and digitalis can worsen bradycardia or conduction problems. [1]

  • Adderall
    caution
    Extended-release clonidine has been studied alongside methylphenidate or amphetamine in children with an incomplete ADHD response. This needs supervised titration and monitoring of sedation, blood pressure and pulse; the trial did not establish equal benefit with every branded formulation. [1][3]
  • Vyvanse
    caution
    Extended-release clonidine has been studied alongside methylphenidate or amphetamine in children with an incomplete ADHD response. This needs supervised titration and monitoring of sedation, blood pressure and pulse; the trial did not establish equal benefit with every branded formulation. [1][3]
  • Concerta
    caution
    Extended-release clonidine has been studied alongside methylphenidate or amphetamine in children with an incomplete ADHD response. This needs supervised titration and monitoring of sedation, blood pressure and pulse; the trial did not establish equal benefit with every branded formulation. [1][3]
  • Ritalin
    caution
    Extended-release clonidine has been studied alongside methylphenidate or amphetamine in children with an incomplete ADHD response. This needs supervised titration and monitoring of sedation, blood pressure and pulse; the trial did not establish equal benefit with every branded formulation. [1][3]

FAQ

Is clonidine a stimulant?
No. It stimulates alpha-2 adrenergic receptors and reduces sympathetic outflow. [1]

References

entry last reviewed 2026-09-21
  1. [1]
  2. [2]
    Clonidine extended-release tablets for pediatric patients with attention-deficit/hyperactivity disorder.
    Jain R, Segal S, Kollins SH et al.J Am Acad Child Adolesc Psychiatry 2011RCT · humanPMID 21241954◌ unreviewed
  3. [3]
    Clonidine extended-release tablets as add-on therapy to psychostimulants in children and adolescents with ADHD.
    Kollins SH, Jain R, Brams M et al.Pediatrics 2011RCT · humanPMID 21555501◌ unreviewed
  4. [4]
  5. [5]