Hydralazine

Written by Sarah Lewis, PharmD
Medically reviewed by Rosanna Sutherby, PharmD on June 4, 2023
Updated on June 16, 2023

This article describes hydralazine’s uses, side effects, and more. You’ll also find some coupon options to help save on the cost of hydralazine.

Hydralazine may cause mild or serious side effects. More common mild side effects of hydralazine and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about hydralazine’s side effects, ask your doctor or pharmacist. You can also read the prescribing information for hydralazine in the “Article resources” section.

Mild side effects

More common mild side effects reported with some forms of hydralazine are listed below. These side effects are likely the same regardless of the form of hydralazine you take or use.

This article doesn’t include all possible mild side effects of the drug. To learn more about hydralazine’s side effects based on the form, see the prescribing information for hydralazine in the “Article resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Mild side effects of hydralazine include:

• diarrhea
• headache
• loss of appetite
• nausea or vomiting
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for hydralazine” section.

Serious side effects

Serious side effects of hydralazine are listed below. This article doesn’t include all possible serious side effects of the drug. To learn more about hydralazine’s side effects, see the drug’s prescribing information in the “Article resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, hydralazine’s serious side effects include:

• abnormal levels of certain blood cells
• changes to mental health, such as severe depression, anxiety, or confusion
• chest pain
• fast heart rate or palpitations (feeling like your heart is fluttering)
• nerve problems
• swelling in the arms or legs due to fluid buildup
• symptoms similar to those caused by lupus (an autoimmune disorder)
• trouble breathing
• trouble urinating
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for hydralazine” section.

Below you’ll find answers to a few commonly asked questions about hydralazine.

What is hydralazine’s mechanism of action? And how long does it take to start working?

Hydralazine’s mechanism of action (how it works) isn’t fully understood. It’s a vasodilator, meaning it likely acts directly on blood vessels to relax them. This lowers pressure inside them.

Hydralazine oral tablet will usually start working within a couple of hours. Hydralazine injection* generally starts to work right away. Its maximum effect on lowering blood pressure usually takes 10–80 minutes.

If you’d like to know more about this, talk with your doctor or pharmacist.

* This form is given as an intramuscular injection (injection into a muscle) or as an intravenous (IV) infusion (injection into your vein given over time).

Does hydralazine come as a brand-name drug?

No, hydralazine is only available as a generic drug. If you’d like to know more about this, talk with your doctor or pharmacist.

Is hydralazine safe for older adults?

Possibly. The drug manufacturer doesn’t give any information about using hydralazine in older adults (ages 65 years or older). But age can affect the safety and dosage of many drugs. If you’re concerned about taking hydralazine given your age, talk with your doctor or pharmacist.

The Food and Drug Administration (FDA) approves prescription drugs such as hydralazine for certain conditions. Approved uses for hydralazine are described below.

Use for high blood pressure

Doctors may prescribe hydralazine oral tablet for treating high blood pressure. They may prescribe hydralazine injection* for treating severe high blood pressure if:

• you can’t take the oral form, or
• there’s an urgent need to lower your blood pressure

Hydralazine is used for this purpose in adults and children.† The oral tablet is usually prescribed as a long-term treatment. The injection is for short-term treatment in a hospital or clinic.

With high blood pressure, people don’t usually have symptoms. But people with high blood pressure are at risk of serious and even fatal events. This includes heart attack and stroke. Lowering blood pressure can help prevent these life threatening events. To know whether you have high blood pressure, it’s important to get regular blood pressure readings. This is often done at most doctor’s appointments.

Hydralazine can be prescribed together with other medications for high blood pressure.

Doctors may not prescribe hydralazine in certain situations, such as for people with heart disease or certain heart valve problems.

*  This form is given as an intramuscular injection (injection into a muscle) or as an intravenous (IV) infusion (injection into your vein given over time).
† Hydralazine has not been studied in children younger than 18 years, but it has been used in children.

Below, you’ll find information about hydralazine’s possible interactions and warnings.

Interactions of hydralazine

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take hydralazine, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for hydralazine” section below.

Warnings for hydralazine

Some people should not take hydralazine and others should take it cautiously.

Hydralazine could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether hydralazine is a safe option for you.

Ask your doctor about specific warnings for hydralazine, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Hydralazine can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to hydralazine or any of its ingredients, your doctor will likely not prescribe hydralazine. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to hydralazine, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of hydralazine

If you take hydralazine by mouth, you should not take more hydralazine than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much hydralazine, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and hydralazine

Information about hydralazine and pregnancy and breastfeeding is described below.

Hydralazine and pregnancy

It’s not known whether hydralazine should be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication.

Hydralazine and breastfeeding

It’s not known whether hydralazine should be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication.

This article describes hydralazine’s uses and side effects, ways to save on cost, and more. Let your doctor know if you have questions about hydralazine or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• What other medications could be used to treat my condition?
• How does hydralazine compare to other medications for my condition?
• What should I do if I miss a dose of hydralazine?

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Hydralazine hydrochloride- hydralazine hydrochloride injection, solution. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/d89d981d-64cf-7321-e053-2995a90aab4a/spl-doc
• Hydralazine hydrochloride- hydralazine hydrochloride tablet. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/493a8b7e-5bb1-4db2-91a7-77ed87864131/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.