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Clorpres Side Effects

Generic Name: chlorthalidone / clonidine

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

For the Consumer

Applies to chlorthalidone / clonidine: oral tablet

In addition to its needed effects, some unwanted effects may be caused by chlorthalidone / clonidine. In the event that any of these side effects do occur, they may require medical attention.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when 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)

Severity: Moderate

If any of the following side effects occur while taking chlorthalidone / clonidine, check with your doctor or nurse as soon as possible:

Signs and symptoms of too much potassium loss
  • Dryness of mouth
  • increased thirst
  • irregular heartbeat
  • mood or mental changes
  • muscle cramps or pain
  • nausea or vomiting
  • weak pulse
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

Minor Side Effects

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

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

Side Effects: Post Treatment

After you stop taking this drug, it is possible that you may still experience side effects that need medical attention. If you notice any of the following side effects check with your doctor immediately:

  • 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.

Not all side effects for Clorpres may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.