Antihistamine Shots (Injections)

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Pharmacy Author: Eni Williams, PharmD, PhD
    Eni Williams, PharmD, PhD

    Dr. Eni Williams graduated from Creighton University in 1988 with a B.S. degree in pharmacy and a Doctor of Pharmacy from Howard University in 1994. She also obtained a Ph.D. in Public Policy in 2009 at the University of Maryland, Baltimore County.

  • Medical and Pharmacy Editor: Charles Patrick Davis, MD, PhD
    Charles Patrick Davis, MD, PhD

    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

What are antihistamine shots, and what are the medical uses for this type of drug?

Antihistamine shots are prescription medications that are used for the rapid medical treatment of conditions such as:

Antihistamine shots also are used to alleviate extra pyramidal symptoms of antipsychotic medications.

Histamine is a chemical that causes many signs and symptoms of allergy. Histamine is released from histamine-storing cells (mast cells) and attaches to other cells that have receptors for histamine on their surfaces. Histamine stimulates the cells to release chemicals that produce effects that we associate with allergy. Antihistamines blocks histamine receptors and thus prevent activation of cells with histamine receptors by histamine.

What are examples of generic and brand names of antihistamine injections available in the US?

Examples of the brand and generic names for this type of medication include:

The formulation of this drug is available by prescription only to treat a patient with a specific condition. It is not available over-the-counter (OTC). Other formulations of antihistamine drugs are available over-the-counter that treat medical conditions such as:

Examples of OTC medicine available over-the-counter include:

What are the side effects of antihistamine shots?

The common side effects of this type of medication include:

Which drugs interact with antihistamine shots?

Antihistamine injections have additive effects if used with alcohol or other central nervous system depressant medications such as:

Effects of antihistamines are prolonged if combined with monoamine oxidase inhibitors (MAOIs) such as:

Antihistamine injections should be used with caution if the patient under medical care and receiving treatment with an MAOI drug.

What formulations of antihistamine injections are available?

  • Prescription antihistamine injections are available in injection form.
  • Diphenhydramine, promethazine, and dimenhydrinate are administered intramuscularly and intravenously.
  • Hydroxyzine hydrochloride is administered only intramuscularly.
  • Antihistamine injections are not recommended for administration via subcutaneous route.

Is it safe to have antihistamine shots during pregnancy or while breastfeeding?

  • FDA lists diphenhydramine and dimenhydrinate as Pregnancy Category B and promethazine as Pregnancy Category C. Hydroxyzine does not have a Pregnancy Category. These categories mean that the safe and effective use of any antihistamine injection drug is not established in during pregnancy; therefore, if a patient is pregnant, medical treatment with this drug should be used only if clearly needed.
  • It is not known whether an injected antihistamine drug enters breast milk; therefore, patients who are pregnant should seek medical advise and use caution before treatment with a prescription antihistamine injection medication in women who are breastfeeding.


Antihistamine shots or injections are prescription drugs used to treat a patient for the rapid treatment of allergic reactions, anxiety, nausea, vomiting, motion sickness, and induce sedation. Side effects of allergy shots include:

Drug interactions, dosage, storage, and pregnancy and breastfeeding safety information should be reviewed prior to using this medication.

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REFERENCE: FDA Prescribing Information.