What Is Chlorthalidone/Clonidine? Uses, Dosage, and What You Need to Know in 2026

Chlorthalidone/clonidine — sold under the brand name Clorpres — was a fixed-dose combination antihypertensive medication that paired two blood pressure drugs into a single tablet. While the combination pill has been permanently discontinued in the United States, both of its components (generic clonidine and generic chlorthalidone) remain widely used medications for hypertension. This guide explains what the drug was, how it was used, what the key safety considerations are, and what patients currently on these components need to know.

What Is Chlorthalidone/Clonidine (Clorpres)?

Clorpres was an oral tablet that combined two distinct antihypertensive drug classes:

Clonidine hydrochloride — A centrally acting alpha-2 adrenergic agonist that lowers blood pressure by reducing sympathetic nervous system activity.

Chlorthalidone — A thiazide-like diuretic (water pill) that reduces blood pressure by lowering blood volume through increased urination.

Together, these two mechanisms provided complementary blood pressure lowering — clonidine working on the brain and nervous system, chlorthalidone working on the kidneys.

FDA-Approved Uses

Clorpres was FDA-approved for the treatment of hypertension (high blood pressure) in adults. It was specifically indicated as a fixed-combination drug for patients who had already been individually titrated on both components and for whom the fixed-combination represented the appropriate doses. It was not intended as initial therapy for hypertension.

Dosage Forms and Strengths

Clorpres was available as oral tablets in three fixed-dose strengths (clonidine/chlorthalidone):

0.1 mg / 15 mg

0.2 mg / 15 mg

0.3 mg / 15 mg

How Was the Dosage Determined?

Clorpres was not used for initial hypertension treatment. The typical sequence was:

A patient was individually titrated on clonidine hydrochloride (usually starting at 0.1 mg twice daily) until an effective dose was established.

Chlorthalidone was separately titrated (usually starting at 25 mg once daily, sometimes 15 mg).

If the effective doses matched one of the three Clorpres tablet strengths, the patient was switched to the combination tablet for convenience.

Maximum daily dose was 0.6 mg clonidine + 30 mg chlorthalidone (two 0.3/15 mg tablets). The medication could be taken once or twice daily depending on the clonidine dose.

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Is Chlorthalidone/Clonidine a Controlled Substance?

No. Neither clonidine (oral antihypertensive tablets) nor chlorthalidone is classified as a controlled substance by the DEA. There are no special prescription requirements, refill restrictions, or scheduling limitations. Any licensed prescriber can write these prescriptions, and they can be called or faxed to a pharmacy like any standard prescription.

Current Status in 2026

Clorpres (chlorthalidone/clonidine) as a fixed-dose combination pill has been permanently discontinued in the United States. The discontinuation was not due to safety or efficacy concerns. Both generic clonidine and generic chlorthalidone remain widely available and affordable as separate prescriptions. Patients formerly on Clorpres are now typically prescribed the two individual generics at equivalent doses.

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Who Was Prescribed Clorpres?

Clorpres was generally prescribed for adult patients with hypertension who:

Required both a centrally-acting agent and a diuretic to control blood pressure

Had already been titrated on both components individually and found the fixed-combination dose appropriate

Preferred a single pill for convenience and adherence

Key Safety Warnings

The most critical safety issue: clonidine must never be stopped abruptly due to risk of severe rebound hypertension. For a full review of side effects and safety warnings, see our Chlorthalidone/Clonidine side effects guide.