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Guide to Antihistamine Medications for Hay Fever

Hay fever, also known as allergic rhinitis, is a common respiratory allergy. Statistics indicate that approximately 20% to 30% of the population in Hong Kong is affected by hay fever. Symptoms of hay fever include sneezing, a runny nose, nasal congestion, and itchy eyes. These symptoms not only affect the quality of sleep but can also impact work and learning. Therefore, understanding how to choose the right medication for hay fever is crucial for improving quality of life. This article will introduce common antihistamines, which are primarily used to treat allergic reactions such as pollen allergies, urticaria, and hay fever. We will compare different types of antihistamines to help readers choose the most suitable treatment plan. 


How Antihistamines Work 

Antihistamines are primarily used to suppress allergic reactions caused by histamine (H1), a chemical released as part of the body's immune response. When allergens such as pollen, dust mites and animal hair/fur are inhaled by susceptible individuals, excessive histamine is released, causing allergic symptoms. Antihistamines work by blocking histamine from binding to its receptors, thus alleviating these symptoms. 


Types of Antihistamines 

First-Generation Antihistamines 

First-generation antihistamines, such as diphenhydramine and chlorpheniramine, were developed early on and are effective in alleviating allergy symptoms. However, as these drugs can cross the blood-brain barrier, they often cause side effects such as drowsiness and lack of concentration. Therefore, special attention is needed when using these medications, especially for those whose work involves more concentration and attentiveness such as driving or operating machinery. 


Second-Generation Antihistamines 

Second-generation antihistamines, such as cetirizine, , and loratadine, have less impact on the central nervous system, thus causing fewer effects on sleepiness and cognitive function. This makes second-generation drugs the preferred choice for many hay fever sufferers. Additionally, these medications have a longer duration of action, typically requiring only once-daily dosing. 


Third-Generation Antihistamines 

Third-generation antihistamines have been further developed from second-generation drugs and feature better properties and fewer side effects. These drugs, including desloratadine and fexofenadine, have lower side effects on the heart, making them safer for patients with cardiac conditions. Third-generation medications also provide rapid and lasting relief with minimal impact on daily activities. 


Choosing and Using Antihistamines 

When choosing the appropriate antihistamine, consider the following aspects: 

  • Severity of Symptoms: Patients with mild to moderate symptoms may be suitable for second or third-generation antihistamines, as they have fewer side effects and do not impact daily activities. Those with severe symptoms may require a stronger prescription medicine or a combination of treatments. 
  • Personal Health Conditions: If the patient has other health issues, such as heart disease or high blood pressure, care should be taken when selecting medications. Third-generation antihistamines may be a better choice due to their minimal cardiac effects. 
  • Compatibility with Daily Life: If work or study requires high concentration, avoid first-generation antihistamines that can cause drowsiness. 
  • Convenience of Medication: Considering the frequency of medication, second and third-generation antihistamines, which usually require only once-daily dosing, are more suitable for a busy lifestyle. 
  • For elderly individuals, second and third generation antihistamines are generally preferred due to their better safety profile and once-daily dosing. 

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Antihistamines Q&A 

Can antihistamines completely cure hay fever? 

A1: Antihistamines are mainly used to control symptoms and cannot cure allergic rhinitis. Long-term management of hay fever may also require avoiding allergens and may involve immunotherapy. Allergen testing may also be considered to identify triggers. 


What should be noted when using antihistamines? 

A2: Avoid combining with alcohol and other substances that can cause drowsiness. If taking other medications, it is best to consult a doctor to avoid drug interactions. 


What happens if antihistamines are taken in excess? 

A3: Overdosing on any type of antihistamine can lead to symptoms such as increased drowsiness, blurred vision, nausea, vomiting, rapid heartbeat, confusion, loss of balance, seizure and coma. Symptoms usually appear within six hours and can worsen over time. Therefore, if you need to use antihistamines frequently or for a long period, you should consult a doctor to ensure safety and monitor for potential side effects. 



Hay fever is a common allergy issue, and antihistamines are often the first choice of treatment for many people. When taking antihistamines, it is best to consult a doctor, follow the doctor's prescription and medication instructions, and avoid increasing the dosage on your own to prevent adverse reactions. Adopting a healthy lifestyle to reduce allergic reactions, such as maintaining indoor cleanliness and avoiding known allergens, is also crucial. Allergen testing may also be considered, especially for individuals with a strong personal and family history of allergies. If you have any questions about hay fever or difficulties with antihistamines, feel free to consult our family doctor for personalised advice. 

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  1. Greiner, A. N., Hellings, P. W., Rotiroti, G., & Scadding, G. K. (2011). Allergic rhinitis. The Lancet, 378(9809), 2112-2122.

  2. Simons, F. E. (2004). Advances in H1-Antihistamines. New England Journal of Medicine, 351(21), 2203-2217.

  3. Wallace, D. V., Dykewicz, M. S., Bernstein, D. I., Blessing-Moore, J., Cox, L., Khan, D. A., Lang, D., Nicklas, R. A., Oppenheimer, J., & Portnoy, J. M. (2008). The diagnosis and management of rhinitis: An updated practice parameter. Journal of Allergy and Clinical Immunology, 122(2), S1-S84.

Topics: General Practice / Family Medicine

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