June 1, 2023

All About Antihistamines: What are they and why do they stop working?

Allergies can be frustrating and uncomfortable, especially when antihistamines are no longer effective in providing relief. While antihistamines are a commonly used medication to alleviate allergy symptoms, there are several reasons why they may not be working for you. In this blog, we will explore the various factors that can contribute to antihistamines not working and provide alternative options for managing allergy symptoms. 

What are antihistamines?

Antihistamines are a type of medication that is commonly used to treat allergy symptoms. They work by blocking the action of histamine, a chemical that is released by the body in response to allergens. Histamine is responsible for many of the symptoms associated with allergies, including itching, runny nose, sneezing, and hives. By blocking the chemical histamine, antihistamines can reduce or eliminate these symptoms.

Different types of antihistamines

Antihistamines are available in both over-the-counter and prescription forms, and come in a variety of formulas, including tablets, capsules, and liquids. There are several different types of antihistamines, including first-generation and second-generation. One of the most widely known and used first generation antihistamines is Benadryl, which contains diphenhydramine and is used to treat a variety of allergy symptoms, including itching, hives, and a runny nose. Second-generation antihistamines, such as Claritin and Zyrtec are other popular over-the-counter antihistamines that are often used to treat seasonal allergies and are known for their non-drowsy formulas.

Prescription antihistamines include Allegra and Xyzal, these medications are often used to treat chronic allergies and are available in extended-release formulas for long-lasting relief. 

While antihistamines can be effective in treating allergy symptoms, it is important to talk to a healthcare provider before starting any new medication. Some antihistamines can cause drowsiness or other side effects, and may interact with other medications or medical conditions.

Nasal Steroids

Nasal steroids are a type of medication commonly used to treat nasal allergies, such as seasonal allergic rhinitis. These medications are available both over-the-counter and by prescription and are typically administered through a nasal spray. 

Nasal steroids work by reducing inflammation in the nasal passages, which can help relieve symptoms such as congestion, sneezing, and a runny nose. They are often preferred over other allergy medications because they are highly effective and have relatively few side effects. Unlike antihistamines, which work by blocking the action of histamine, nasal steroids target the underlying inflammation that causes allergy symptoms.

Nasal sprays are a common form of medication used to treat allergies, nasal congestion, and other respiratory conditions. While they are generally safe and effective when used as directed, they can have some potential side effects, including:

  • Nasal irritation or dryness
  • Nosebleeds
  • Headaches
  • Nausea
  • Sneezing
  • Bad taste or smell
  • Dizziness
  • Throat irritation or coughing
  • Increased risk of infection (if the spray is not used properly)

It is important to follow the directions for use carefully, and to talk to a healthcare provider if you experience any side effects or have any concerns about using a nasal spray. In some cases, alternative treatments or medications may be more appropriate for managing your symptoms.


Decongestants are a type of medication used to relieve nasal congestion caused by allergies, colds, or other respiratory illnesses. They work by reducing swelling in the nasal passages, which can help open up the airways and improve breathing. Decongestants can be taken orally, as a pill or liquid, or applied topically, as a nasal spray.

Oral decongestants, such as phenylephrine and pseudoephedrine, work by constricting blood vessels in the nasal passages, which reduces swelling and congestion. They are often combined with other medications, such as antihistamines, to provide relief from multiple allergy symptoms.

Nasal decongestants, such as oxymetazoline and phenylephrine, work by directly targeting the nasal tissues and reducing inflammation. They are typically used for short-term relief of nasal congestion, and should not be used for more than a few days in a row to avoid rebound congestion.

 While decongestants can be effective in relieving nasal congestion, they can have some potential side effects, including increased blood pressure, rapid heartbeat, dizziness, and difficulty sleeping. 

How do antihistamines work?

Antihistamines are a class of medication that is commonly used to treat allergies and other conditions caused by the release of histamine in the body. Histamine is a chemical that plays a key role in the body's immune response, causing the symptoms associated with allergies such as sneezing, itching, and a runny nose. Antihistamines work by blocking the effects of histamine, preventing it from binding to its receptors and triggering the allergic response. This helps reduce symptoms such as itching and inflammation and can also help relieve symptoms associated with other conditions such as motion sickness and insomnia. Some antihistamines also have sedative effects, which can be helpful for promoting relaxation and improving sleep. Overall, antihistamines are an option for managing a variety of allergic and other conditions, and they are widely available over-the-counter and by prescription from healthcare providers.


Why do antihistamines stop working?

Does it feel like your antihistamine medication isn’t working like it used to? Some individuals may experience a decrease in the effectiveness of antihistamines over time, which can be frustrating and concerning. There are several reasons why antihistamines may stop working. 


One of the main concerns with long-term antihistamine use is the risk of developing tolerance. When taken regularly, the body can become accustomed to the medication, leading to a decreased effectiveness over time. This can result in the need for higher doses or switching to a different medication to achieve the same relief.


Another possibility is that the individual may have been exposed to a new allergen or a higher level of an existing allergen, which can trigger a more severe allergic reaction that the antihistamine cannot fully manage. Certain medications or medical conditions may also interfere with the effectiveness of antihistamines, making them less effective over time.

Climate Change

It is possible that the changing climate is impacting the effectiveness of your antihistamines. As the weather continues to warm up and winters become milder, the growing seasons of allergens such as trees and grasses are prolonged, resulting in longer periods of pollen production. Consequently, the allergy season becomes more severe, with higher concentrations of potent allergens. This increased severity of the allergy season may be the reason why your antihistamines appear to be ineffective.


Stress is a common occurrence in our daily lives, and it can have a significant impact on our health. One of the ways that stress can affect our bodies is by disrupting our immune system. When we experience stress, our bodies release stress hormones such as cortisol, which can alter the way our immune system functions. This alteration can cause our immune system to become overactive and trigger allergic reactions even when we are exposed to harmless substances.

It is important to note that while tolerance to antihistamines can occur, it is not a universal experience. Many individuals continue to benefit from the medication even after long-term use. If antihistamines are no longer effective, it is important to speak with a healthcare provider to determine the underlying cause and to explore alternative treatment options.

Side effects of antihistamines?

Antihistamines can have several side effects. The side effects of antihistamines can vary depending on the type of antihistamine taken. The most common side effect of first-generation antihistamines is sedation, which makes one feel drowsy or sleepy. Some of the other common side effects of antihistamines include 

  • dry mouth
  • dry eyes
  • blurred or double vision
  • dizziness
  • headache
  • congestion
  • rapid heart rate
  • difficulty urinating
  • constipation

Long-term effects of antihistamines?

Additionally, long-term use of antihistamines has been linked to an increased risk of dementia and depression. Some antihistamines have been also associated with weight gain, particularly in individuals who use them regularly. While the mechanism behind this effect is not entirely understood, it is thought to be related to the medication's impact on appetite and metabolism.


Did you know about the side effects antihistamines can have? Learn more about long-term treatment options by visiting aspireallergy.com

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What to do when antihistamines stop working

If antihistamines stop working, it can be frustrating and concerning, but there are several options to explore. One option is to switch to a different type of antihistamine, as different medications may work better for different individuals. Another option is to combine antihistamines with other medications, such as decongestants or corticosteroids, to manage more severe symptoms.

In addition to medication, there are several lifestyle changes that can help manage allergies. These include:

  • Avoiding allergens as much as possible
  • Using HEPA air purifiers and filters 
  • Keeping the home clean and free of dust and other allergens
  • Nasal irrigation with saline solution can also help flush out allergens from the nasal passages and improve symptoms
  • In some cases, immunotherapy, or allergy shots, may be recommended to help the body build up a tolerance to allergens over time
  • Consider switching to a different type of antihistamine 
  • Combine antihistamines with other medications, such as decongestants or corticosteroids, to manage more severe symptoms

It’s important to continue treatment for allergies, as untreated allergies can lead to complications such as sinus infections and respiratory problems. By exploring different treatment options and making lifestyle changes, you can effectively manage your allergies and improve your overall quality of life.

Alternative medications for antihistamines

While there is no cure for allergies, treatments such as antihistamines, immunotherapy, and avoidance of allergens can help manage symptoms and improve quality of life for those affected by this condition. For individuals who are unable to take antihistamines or who experience a decrease in their effectiveness, there are several alternative options available. 

Another alternative option is immunotherapy, or allergy shots. Allergy shots work by exposing the body to small amounts of an allergen over time, gradually building up a tolerance to the allergen, and reducing allergy symptoms. This treatment can be effective for individuals with severe allergies or those who are unable to manage their symptoms with other medications.

Allergy drops, also known as sublingual immunotherapy, are a promising alternative option for individuals who experience allergies and find that their antihistamines are no longer effective. Unlike antihistamines, which only provide temporary relief from allergy symptoms, allergy drops work to desensitize the immune system to allergens, thus reducing the severity of symptoms over time. One of the main benefits of allergy drops is their convenience and ease of use. They can be administered at home, eliminating the need for frequent doctor visits or injections. Additionally, they are safe and effective for both adults and children, making them a viable treatment option for the whole family.

Exact Immunoplasty, also known as allergen-specific immunotherapy, is an effective alternative option for individuals who experience allergies and find that their antihistamines are no longer effective. This treatment involves 3 injections of allergens into the body over the span of eight weeks. The goal is to help the immune system build up a tolerance to the allergen, reducing the severity of the allergic reaction when exposed to it in the future. One of the main benefits of exact immunotherapy is its long-term effectiveness. Unlike antihistamines, which only provide temporary relief from allergy symptoms, exact immunotherapy can provide a permanent solution to allergies.

How Aspire Allergy and Sinus can help 

At Aspire Allergy & Sinus we believe that allergies should be treated at the root cause, not just masking symptoms. We specialize in long-term allergy relief with treatment plans that are customized and curated to your needs. Our expert team of board-certified allergists offer a range of treatment options to help identify, manage and treat allergies. If you find your antihistamines not providing the relief you deserve, book an appointment today

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