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Clorpres Side Effects

Generic Name: chlorthalidone / clonidine

Note: This document contains side effect information about chlorthalidone / clonidine. Some of the dosage forms listed on this page may not apply to the brand name Clorpres.

For the Consumer

Applies to chlorthalidone / clonidine: oral tablet

Along with its needed effects, chlorthalidone/clonidine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking chlorthalidone / clonidine:

Signs and symptoms of overdose

  • Difficulty in breathing
  • dizziness (extreme) or faintness
  • feeling cold
  • pinpoint pupils of eyes
  • slow heartbeat
  • unusual tiredness or weakness (extreme)

Check with your doctor as soon as possible if any of the following side effects occur while taking chlorthalidone / clonidine:

Signs and symptoms of too much potassium loss

Signs and symptoms of too much sodium loss

  • Confusion
  • convulsions (seizures)
  • decreased mental activity
  • irritability
  • muscle cramps
  • unusual tiredness or weakness

Less common

  • Mental depression
  • swelling of feet and lower legs


  • Black, tarry stools
  • blood in urine or stools
  • cough or hoarseness
  • fever or chills
  • joint pain
  • lower back or side pain
  • paleness or cold feeling in fingertips and toes
  • pinpoint red spots on skin
  • skin rash or hives
  • stomach pain (severe) with nausea and vomiting
  • unusual bleeding or bruising
  • vivid dreams or nightmares
  • yellow eyes or skin

Some side effects of chlorthalidone / clonidine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Constipation
  • dizziness
  • drowsiness
  • dryness of mouth
  • unusual tiredness or weakness

Less common

  • Decreased sexual ability
  • diarrhea
  • dizziness or lightheadedness when getting up from a lying or sitting position
  • dry, itching, or burning eyes
  • increased sensitivity of skin to sunlight
  • loss of appetite
  • nausea or vomiting
  • nervousness
  • upset stomach

After you stop using this medicine, it may still produce some side effects that need attention. During this period of time, check with your doctor immediately if you notice the following side effects:

  • Anxiety or tenseness
  • chest pain
  • fast or pounding heartbeat
  • headache
  • increased salivation
  • nausea
  • nervousness
  • restlessness
  • shaking or trembling of hands and fingers
  • stomach cramps
  • sweating
  • trouble in sleeping
  • vomiting

For Healthcare Professionals

Applies to chlorthalidone / clonidine: oral tablet


The most frequent adverse reactions were dry mouth, drowsiness, dizziness, constipation, and sedation.[Ref]


Very common (10% or more): Dry mouth (up to 40%), constipation (up to 10%)

Frequency not reported: Gastric irritation, nausea, vomiting, cramping, diarrhea, constipation, pancreatitis

Common (1% to 10%): Nausea, vomiting
Frequency not reported: Parotitis[Ref]

Nervous system

Very common (10% or more): Drowsiness (up to 33%), dizziness (up to 16%), sedation (up to 10%)

Frequency not reported: Dizziness, vertigo, paresthesias, headache

Common (1% to 10%): Headache[Ref]


Frequency not reported: Weakness

Very common (10% or more): Weakness (up to 10%)
Common (1% to 10%): Malaise, fatigue, discontinuation syndrome
Uncommon (0.1% to 1%): Gynecomastia
Frequency not reported: Dryness, increased sensitivity to alcohol, fever[Ref]


Frequency not reported: Necrotizing angiitis, orthostatic hypotension

Common (1% to 10%): Orthostatic symptoms
Uncommon (0.1% to 1%): Palpitations, tachycardia, bradycardia
Frequency not reported: Raynaud's phenomenon, congestive heart failure, ECG abnormalities, sinus bradycardia, atrioventricular block, pallor[Ref]


Frequency not reported: Purpura, photosensitivity, rash, urticaria, Lyell's syndrome

Common (1% to 10%): Rash
Uncommon (0.1% to 1%): Pruritus, hives, angioneurotic edema, urticaria, alopecia[Ref]


Frequency not reported: Glycosuria, impotence

Common (1% to 10%): Sexual activity decreased, impotence, nocturia
Uncommon (0.1% to 1%): Difficulty in micturition, urinary retention[Ref]


Frequency not reported: Leukopenia, agranulocytosis, thrombocytopenia, aplastic anemia

Frequency not reported: Weakly positive Coombs' test[Ref]


Frequency not reported: Intrahepatic cholestatic jaundice

Common (1% to 10%): Mild transient abnormalities in liver function tests
Frequency not reported: Hepatitis[Ref]


Frequency not reported: Anorexia, hyperglycemia, hyperuricemia

Common (1% to 10%): Anorexia, weight gain
Frequency not reported: Transient elevation of blood glucose[Ref]


Frequency not reported: Muscle spasm

Uncommon (0.1% to 1%): Muscle or joint pain, cramps of the lower limbs
Frequency not reported: Transient elevation of serum creatine phosphokinase[Ref]


Frequency not reported: Xanthopsia

Frequency not reported: Burning of the eyes, blurred vision[Ref]


Frequency not reported: Restlessness

Common (1% to 10%): Nervousness, agitation, mental depression, loss of libido
Uncommon (0.1% to 1%): Insomnia
Frequency not reported: Vivid dreams, nightmares, behavioral changes, restlessness, anxiety, visual and auditory hallucinations, delirium[Ref]


Frequency not reported: Dryness of the nasal mucosa[Ref]


1. "Product Information. Combipres (clonidine-chlorthalidone)." Boehringer-Ingelheim, Ridgefield, CT.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.