Antihistamines for Allergies: Benefits, Risks, and Replacements


What are antihistamines?

Antihistamines are medications commonly used to treat allergy symptoms like sneezing, itchiness, and wheezing. They block the release of histamine, a substance produced by cells in the body in response to allergens like pollen, pet dander, and dust mites. They also treat other conditions caused by motion sickness.

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Antihistamines have been the go-to solution for many people suffering from allergies, but they frequently don’t provide enough relief or they come with uncomfortable side effects. Read more to learn about the different antihistamine types, side effects, and alternatives to have all the information you need to make informed decisions about your allergy treatment and management.

What Is an Antihistamine?

Antihistamines are medications commonly used to manage allergy symptoms, including sneezing, congestion, and postnasal drip. The immune system releases histamine when it comes into contact with allergens, bacteria, viruses, and other pathogens. Antihistamines are used to reduce the symptoms that histamine causes.

How Do Antihistamines Help Allergies?

Antihistamines help manage allergies by blocking the effects of histamine on the body. Histamine is a chemical released by the immune system when exposed to allergens as part of a defense response. Antihistamines prevent histamine from binding to different receptors throughout the body, reducing the allergy symptoms that the release of histamine causes.

Histamine plays a key role in the immune system by triggering inflammation and other responses that help the body fight off infections and other threats. However, it can also cause a variety of symptoms, such as itching, sneezing, runny nose, and hives, when released in excessive amounts or inappropriately.

For people with allergies, the body mistakes harmless substances like pollen, pet dander, dust mites, or mold for a threat and produces histamine, leading to an allergic reaction. Antihistamines work by blocking histamine receptors on these cells, reducing the body’s physical response to allergens.

When histamines bind to these receptors, they trigger several allergic reactions, such as expanding blood vessels and causing smooth muscle tissues to contract. By blocking H1 histamine receptors, antihistamines help alleviate these symptoms and treat other conditions related to allergies, such as hay fever, hives, allergic conjunctivitis, eczema, and reactions to insect bites or stings.

What Are First and Second-Generation Antihistamines?

Antihistamines are categorized into two groups: first and second-generation. First-generation antihistamines were some of the first to be developed and frequently cause side effects including drowsiness and dizziness. Second-generation antihistamines are newer and are typically less sedating than first-generation antihistamines.

First-Generation Antihistamines

First-generation antihistamines work by blocking histamine receptors in the brain and the body through the spinal cord. As such, their defining characteristic is that they cause drowsiness and dizziness because they use the blood-brain barrier to fight pathogens and allergens.

First-generation antihistamines are often used to treat nausea, motion sickness, short-term symptoms of allergies, or allergic reactions. Some examples of first-generation antihistamines include:

  • Diphenhydramine (Nytol, Benadryl, Sominex)
  • Dimenhydrinate (Dramamine)
  • Doxylamine (Unisom, Vicks NyQuil)

Most drugs in this class often take effect around 30-60 minutes after consumption and may last 4-6 hours. These medications can cause several different side effects, so it’s recommended to avoid taking any medications in this class if you suffer from any of the following conditions:

  • Asthma
  • Heart disease
  • Thyroid disease
  • Glaucoma
  • Chronic bronchitis
  • High blood pressure
  • Difficulty with urination
  • Emphysema

Second-Generation Antihistamines

Second-generation antihistamines selectively target histamine receptors in the body and have a reduced risk of sedation and other side effects.

Medications in this group are more effective than first-generation antihistamines and have fewer side effects. They are administered nasally, orally, or through an eye drop and can reduce symptoms for up to 24 hours.

Examples of second-generation antihistamines include:

  • Cetirizine (Zyrtec)
  • Loratadine (Claritin)
  • Fexofenadine (Allegra)
  • Desloratadine (Clarinex)

Both first and second-generation antihistamines are relatively effective at temporarily managing allergy symptoms, so the choice between the two depends on the potential side effects, the severity of your symptoms, and other individual factors like your age, medical history, and what medications you are taking now.

Types of Antihistamines for Allergies

There are several different types of antihistamines available for both first-generation and second-generation. Some of the most common types include:

Diphenhydramine (Benadryl)

Diphenhydramine, a first-generation antihistamine, is commonly used to treat allergic reactions like hives, itching, and nasal congestion. It’s available in various forms, including tablets, capsules, liquids, and topical creams. It is often sold under the brand name Benadryl and is available over-the-counter (OTC) at most pharmacies and drug stores.

While diphenhydramine is generally considered safe when taken as directed, it can cause side effects in some people. Drowsiness is the most common side effect, which can be particularly problematic for people who need to drive or operate heavy machinery. Other possible side effects include:

  • Dry mouth
  • Blurred vision
  • Constipation
  • Difficulty urinating

Because of its sedative effects, diphenhydramine is sometimes used as a sleep aid, either alone or in combination with other medications like acetaminophen or ibuprofen. However, it's important to use caution when using diphenhydramine as a sleep aid, as it can lead to drowsiness or impaired motor function and may also interact with other medications and cause adverse effects.


Chlorpheniramine relieves itchy, red, watery eyes, itchy nose, sneezing, and runny nose caused by allergies. It also helps control the symptoms of the common cold, speeding the recovery process.

Chlorpheniramine is available in tablet and liquid form and is often sold under brand names such as Chlor-Trimeton or Aller-Chlor. You can get it OTC from most drug stores or pharmacies. While chlorpheniramine can be fast-acting, similar to other allergy medications, there are several side effects this medication can cause, including:

  • Nausea
  • Drowsiness and dizziness
  • Headaches
  • Dry mouth
  • Blurred vision
  • Difficulty concentrating

Fortunately, chlorpheniramine is considered safe when taken as directed. Still, it's important to talk to your healthcare provider before starting any new medication, particularly if you have any medical conditions or you’re taking other medications.

Cetirizine (Zyrtec)

Cetirizine, commonly sold under the brand name Zyrtec, is a second-generation antihistamine used to treat various allergic reactions, including hay fever, hives, seasonal allergies, and allergic conjunctivitis. It is available in the form of tablets, chewable tablets, and oral syrup. And unlike some first-generation antihistamines, cetirizine is less likely to cause drowsiness or impair motor function.

Cetirizine usually takes around 20 minutes to one hour to start working, and its effects can last up to 24 hours. It is important to take the medication as directed, typically once per day, to achieve maximum benefit.

Some side effects of cetirizine include:

  • Dry mouth
  • Headaches
  • Diarrhea
  • Nausea
  • Dizziness
  • Sore throat
  • Blocked and runny nose
  • Excessive Sneezing

Desloratadine (Clarinex)

Desloratadine (Clarinex) is a second-generation antihistamine used to relieve allergy symptoms such as watery eyes, runny nose, itching eyes or nose, sneezing, hives, and itching. Desloratadine is commonly used to treat symptoms of hay fever and skin hives.

The time it takes for desloratadine to work may vary depending on the individual and the severity of their symptoms. However, it is generally expected to provide relief within a few hours of taking the medication. Similar to other antihistamines, desloratadine can cause several different side effects such as:

  • Dizziness and headaches
  • Nausea
  • Sleepiness and extreme tiredness
  • Muscle pain
  • Sore throat and dry mouth
  • Painful menstruation
  • Rash, itchiness, and hives
  • Swelling of the throat, face, lips, tongue, hands, eyes, feet, and ankles.
  • Difficulty swallowing and breathing

It is important to follow the instructions provided by your doctor or pharmacist when using Clarinex. If you experience any of the above side effects, stop taking Desloratadine immediately and call your doctor.

Who Can Take Antihistamines?

Antihistamines are generally considered safe for most people, including adults, children over the age of 2, and older individuals. However, it’s essential to consult with a doctor or pharmacist before taking antihistamines as they may interact with other medications or be unsuitable for people with certain conditions.

You should also talk to your healthcare provider if you want to take antihistamines while pregnant or breastfeeding or if you suffer from conditions such as heart disease, diabetes, or high blood pressure.

How to Take Antihistamines?

To take antihistamines, follow the instructions on the label or as directed by a healthcare provider. Take the medication with a glass of water, with or without food, depending on the specific instructions. Do not take more than the recommended dose, as it can increase the risk of side effects.

If you are taking OTC antihistamines, be aware of any other medications you may be taking, as well as any medical conditions you may have, to avoid potential interactions or complications. If you have any questions or concerns, talk to your healthcare provider.

Remember, you should never take two or more antihistamines together unless directed by your doctor.

What Are the Side Effects and Risks?

Antihistamines have many potential risks and side effects. Drowsiness is the most common side effect, which can affect your ability to drive or operate heavy machinery. Other common side effects include dry mouth, headache, blurred vision, and dizziness.

Antihistamines may also interact with other medications, including prescription drugs and OTC supplements, and may worsen certain medical conditions, such as glaucoma, asthma, or prostate problems. It's important to talk to your healthcare provider before taking antihistamines, especially if you have any medical conditions or are taking other medications.

What Are the Best Antihistamine Alternatives?

While antihistamines are a popular treatment for allergies, they frequently don’t provide enough relief or cause unwanted side effects. Several alternatives can help reduce your allergy symptoms.

Mast Cell Stabilizers

Mast cell stabilizers prevent the release of histamine and other chemicals from mast cells, which are the immune cells involved in allergic reactions. These medications are typically used to prevent or reduce symptoms of conditions like allergic rhinitis, asthma, and eczema.

Unlike antihistamines, which block the effects of histamine after it has been released, mast cell stabilizers work to prevent the release of histamine and other inflammatory mediators in the first place. This makes them particularly effective for preventing allergic reactions rather than treating symptoms after they have already started.


Leukotriene inhibitors are a medication used to manage asthma and allergic rhinitis symptoms. They work by blocking the action of leukotrienes, which are chemicals released by the body's immune system in response to an allergen.

Leukotrienes are involved in causing inflammation, swelling, and tightening of airways, which can lead to asthma symptoms like wheezing, coughing, and shortness of breath, as well as allergic rhinitis symptoms like sneezing, runny nose, and nasal congestion. By blocking the action of leukotrienes, these medications help reduce inflammation and improve breathing.

Sublingual Immunotherapy

Sublingual immunotherapy is a type of allergy immunotherapy that involves introducing small doses of allergens to your body to desensitize the immune system. Over time your body builds up a tolerance and stops reacting when exposed to your allergy triggers. This results in long-term relief from your allergy symptoms. Sublingual immunotherapy can provide long-term relief from seasonal and environmental allergies like pollen, dust mites, mold, and pet dander.

Take Our Allergy Assessment

If you’re tired of antihistamines not working or causing unwanted side effects, Wyndly can help. Our allergy doctors will work with you to create a personalized treatment plan that will provide long-term relief from your allergies. See if Wyndly is right for you by taking our quick online allergy assessment today!

Frequently Asked Questions

How Often Can You Take Antihistamines?

How often you take antihistamines depends on the type of antihistamines you are using. Some antihistamines are taken every 4 to 6 hours, while others are taken every 12 to 24 hours. For individuals with daily allergy symptoms, it is generally safe to take antihistamines every day.

It is essential to consult the drug label and your healthcare provider for specific instructions on how often and how long you should take an antihistamine.

If you take an antihistamine frequently or daily, your healthcare provider may recommend a second-generation antihistamine, as they are less likely to cause side effects like sleepiness and fatigue.

Always follow the recommended dosage and instructions provided by your doctor or pharmacist to avoid potential side effects or interactions with other medications.

How Many Antihistamines Can I Take in 24 Hours?

The maximum amount of antihistamine you can take in 24 hours depends on the specific type of drug and your age. It is essential to consult the drug label and your healthcare provider for specific instructions on the maximum dosage for the antihistamine you are using.

Always follow the recommended dosage and instructions provided by your doctor or pharmacist to avoid potential side effects or interactions with other medications.

Do Antihistamines Make You Drowsy?

Yes, many antihistamines can cause drowsiness, particularly first-generation antihistamines such as diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton). Second-generation antihistamines such as cetirizine (Zyrtec) and loratadine (Claritin) are less likely to cause drowsiness. The degree of drowsiness can vary depending on the individual and the specific medication and dosage.

Do Antihistamines Raise Blood Pressure?

Some antihistamines can cause a temporary increase in blood pressure, although the effect usually does not pose a significant risk to most people. However, this can be detrimental to people with high blood pressure or those on any high-blood pressure medications.

Can Children Take Antihistamines?

Yes, children can typically take antihistamines safely. However, it's essential to consult with your pediatrician or primary healthcare provider before giving your child any type of antihistamine. You should also avoid giving children under the age of six any first-generation or sedating allergy medications as they can cause life-threatening side effects.

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