September 2026

What the T4 Marking on a Pill Identifies

By Your Health Magazine Health Information Team

You find a loose tablet in a drawer or notice that a prescription refill looks different from the pills you received last month. The only readable marking is “T4.” Is it a thyroid medicine, a blood pressure drug, or something else? The answer depends on more than those two characters.

In the United States, an ivory or white, oval tablet marked T4 is commonly identified as enalapril maleate and hydrochlorothiazide, containing 5 mg of enalapril maleate and 12.5 mg of hydrochlorothiazide. It is a prescription combination used to treat high blood pressure. However, T4 is not a universally unique marking by itself. Other tablets can display the same or a similar imprint, so color, shape, size, markings on both sides, and the original container all matter.

What Does the T4 Imprint Usually Identify?

The pill T4 most often sought by readers is an approximately 8-millimeter, ivory-to-white, oval tablet manufactured for the U.S. market. Its two active ingredients lower blood pressure in different ways:

Enalapril is an angiotensin-converting enzyme, or ACE, inhibitor. It helps relax blood vessels by reducing the production of a substance that causes them to narrow.
Hydrochlorothiazide is a thiazide diuretic, sometimes called a water pill. It helps the kidneys remove additional sodium and water through urine.

Combining these actions can improve blood pressure control when a clinician determines that both medicines are appropriate. This fixed-dose product is not generally intended as the first treatment a person receives for high blood pressure. It may be prescribed after a healthcare professional has assessed how the patient responds to the individual components or other therapies.

Why the Imprint Alone Is Not Enough

The Food and Drug Administration requires most solid oral medications marketed in the United States to carry a code imprint. The code is meant to be considered together with the pill’s color, shape, and size. Reading only “T4” can therefore lead to the wrong conclusion.

For example, a pink, capsule-shaped extended-release tablet marked T4 has been listed as paliperidone 9 mg, a prescription antipsychotic used in the treatment of schizophrenia and schizoaffective disorder. Certain levothyroxine products also carry a marking that looks like “T 4” or “T|4,” but those tablets include a separate number indicating their strength and come in different colors.

Before accepting any pill identification, check:

Every letter, number, line, and logo on both sides
Whether the tablet is round, oval, capsule-shaped, or another shape
Its exact color, including whether it appears white, ivory, pink, or another shade
Whether it is scored and whether the score is part of the imprint
The prescription label, manufacturer information, and physical description on the bottle

If the appearance does not match the pharmacy label, do not take the tablet until a pharmacist confirms it. Lighting, wear, and a partially broken pill can also make an imprint easy to misread.

What to Expect From Enalapril and Hydrochlorothiazide

When the pill has been positively identified as the white or ivory oval T4 blood pressure tablet, its effects may be noticeable in everyday routines. Hydrochlorothiazide can increase urination, particularly after the medicine is taken. Enalapril and hydrochlorothiazide may also cause dizziness, headache, fatigue, nausea, muscle cramps, or a persistent dry cough.

Because the combination lowers blood pressure, some people feel lightheaded when standing up quickly. Hot weather, heavy sweating, vomiting, diarrhea, or inadequate fluid intake may increase the likelihood of dehydration or an excessive drop in blood pressure. A healthcare professional can advise how to manage these situations without changing the medication independently.

The medicine may affect kidney function and the balance of sodium, potassium, and other electrolytes. Clinicians may therefore order blood tests and monitor blood pressure during treatment. Keeping follow-up appointments is important even when high blood pressure causes no obvious symptoms.

Important Warnings and Interactions

Enalapril-containing medications have a boxed warning for fetal toxicity. They can injure a developing fetus and should not be used during pregnancy. Anyone who becomes pregnant while taking an enalapril product should contact the prescribing clinician promptly rather than waiting for a routine appointment.

A rare but potentially life-threatening reaction called angioedema can cause swelling of the face, lips, tongue, or throat. It may develop at any point during ACE inhibitor treatment, even if the medication was previously tolerated.

Medication interactions are another reason not to take an unidentified pill. Potassium supplements, potassium-containing salt substitutes, potassium-sparing diuretics, lithium, other blood pressure medicines, and nonsteroidal anti-inflammatory drugs such as ibuprofen or naproxen may require special consideration or monitoring. Patients should give their pharmacist and prescriber a complete list of prescription drugs, over-the-counter medicines, vitamins, and supplements.

Reliable consumer drug information is available through the National Library of Medicine’s medication information resource, but online descriptions should support—not replace—verification by a pharmacist.

What If You Found the Pill or Someone Swallowed It?

Do not taste, split, crush, or take a loose pill simply to determine what it is. Place it in a secure container away from children, pets, and anyone who might mistake it for their medication. A local pharmacist can often examine the imprint and compare it with current drug-identification records.

If someone may have swallowed an unknown tablet, contact Poison Control in the United States at 1-800-222-1222, even if no symptoms have appeared. Be prepared to describe the imprint, color, shape, estimated number of pills involved, time of exposure, and the person’s age and symptoms. Do not induce vomiting unless a healthcare professional specifically directs you to do so.

Loose or unidentified medications deserve particular caution in homes where substance use is a concern. Understanding the risks associated with unidentified L484 pills and addiction can reinforce why appearance alone should never be treated as proof of a pill’s contents.

When to Seek Care

Call 911 for trouble breathing, swelling of the tongue or throat, collapse, a seizure, severe confusion, or inability to awaken the person. Urgent evaluation is also appropriate after an unknown-pill exposure accompanied by fainting, severe weakness, chest pain, an irregular heartbeat, or persistent vomiting.

If a confirmed T4 blood pressure tablet causes ongoing dizziness, a troublesome dry cough, muscle weakness or cramps, unusually low urine output, or other new symptoms, contact the prescribing physician, primary care clinician, or pharmacist. Pregnant patients or those planning pregnancy should speak with the prescriber promptly. Do not stop or alter a prescribed medication without professional guidance unless emergency personnel instruct otherwise.

The Bottom Line

A white or ivory oval pill marked T4 commonly identifies enalapril maleate and hydrochlorothiazide 5 mg/12.5 mg, a prescription treatment for high blood pressure. But a pink capsule-shaped T4 tablet and medications carrying additional T4-related markings may contain entirely different drugs. Confirm the complete appearance and packaging with a pharmacist before taking any uncertain medication.