Generic Name: Clonidine.

Trade Name    : Clonidine , Catapres.

Drug Class      : Selective alpha2 – Adrenoceptor Agonists , ADHD Agents.

Forms of The Drug

  1. Injectable Solution:  100mcg/mL , 500mcg/mL.
  2. Patch, Extended-Release: 0.1mg/day , 0.2mg/day, 0.3mg/day.
  3. Tablet, Immediate-Release: 0.1mg , 0.2mg, 0.3mg.
  4. Tablet, Extended-Release: 0.1mg.

Mechanism of Action

Clonidine is classified as an alpha-2 adrenergic agonist. This means it binds to and activates alpha-2 adrenergic receptors located in the central nervous system. These receptors are part of the autonomic nervous system, which controls involuntary bodily functions such as heart rate, blood vessel constriction, and other stress responses. The primary mechanisms of action of clonidine include:

  1. Central Nervous System Effects: Clonidine acts centrally in the brain by stimulating alpha-2 adrenergic receptors in specific regions. When these receptors are activated, it results in reduced sympathetic nervous system activity. The sympathetic nervous system is responsible for the “fight or flight” response, which includes increased heart rate and blood pressure. By inhibiting the activity of this system, clonidine leads to a decrease in heart rate and a relaxation of blood vessels, leading to a reduction in blood pressure.
  2. Blood Vessel Relaxation: Clonidine’s activation of alpha-2 receptors in the blood vessels causes relaxation of the smooth muscle within the vessel walls. This relaxation results in vasodilation, or the widening of blood vessels. As blood vessels dilate, there is less resistance to blood flow, leading to a decrease in blood pressure.
  3. Suppression of Norepinephrine Release: Clonidine also works by reducing the release of norepinephrine, a neurotransmitter and stress hormone. Norepinephrine is involved in the transmission of nerve impulses in the sympathetic nervous system. By inhibiting its release, clonidine further reduces sympathetic nervous system activity, leading to lowered blood pressure and a decrease in stress responses.
  4. Feedback Mechanism: The body has feedback mechanisms to regulate blood pressure. Clonidine’s action on alpha-2 receptors in the brainstem can influence these feedback mechanisms, leading to a decrease in the signals that would normally increase blood pressure.


  1. Hypertension (High Blood Pressure).
  2. Attention Deficit Hyperactivity Disorder (ADHD).
  3. Opioid Withdrawal.
  4. Pain Disorders.
  5. Tourette syndrome and Tic Disorders.
  6. Menopausal Symptoms.


  1. Hypersensitivity to Clonidine.
  2. Severe Bradycardia (Slow Heart Rate).
  3. Heart Block.
  4. Hypotension (Low Blood Pressure).
  5. Recent Myocardial Infarction (Heart Attack).
  6. Cerebrovascular Disease.
  7. Renal Impairment.
  8. Pregnancy and Breastfeeding.
  9. Combining with Certain Medications.
  10. Withdrawal from Clonidine.

Side Effects

  1. Skin reactions; patch (15-50%).
  2. Dry mouth (40%).
  3. Somnolence (19-38%).
  4. Headache (19-29%).
  5. Fatigue (13-24%).
  6. Drowsiness (33%).
  7. Dizziness (13-16%).
  8. Hypotension, epidural (45%).
  9. Postural hypotension, epidural (32%).
  10. Anxiety (11%).
  11. Constipation (10%).
  12. Sedation (10%).
  13. Nausea/vomiting, PO (5%).
  14. Malaise (3%).
  15. Orthostatic hypotension (3%).
  16. Anorexia, PO (1%).
  17. Abnormal LFTs (1%).
  18. Rash (1%).
  19. Weight gain, PO (1%).

Drug Interaction

Other drugs that can interact with it.

  1. Beta-Blockers: Combining clonidine with beta-blockers (e.g., propranolol, metoprolol).
  2. Calcium Channel Blockers: Similar to beta-blockers, calcium channel blockers (e.g., verapamil, diltiazem).
  3. Tricyclic Antidepressants (TCAs).
  4. Monoamine Oxidase Inhibitors (MAOIs).
  5. Sedatives and CNS Depressants.
  6. Antihypertensive Medications.
  7. Sympathomimetic Agents: Medications that stimulate the sympathetic nervous system, such as decongestants and some bronchodilators.
  8. Lithium.
  9. Non-steroidal Anti-Inflammatory Drugs (NSAIDs).
  10. Guanfacine.
  11. Antidiabetic Medications.
  12. Herbal Supplements.


  1. Pregnancy: Category C
  2. Lactation: Clonidine can pass into breast milk, and its use during lactation (breastfeeding) should be carefully considered.

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