Antihistamines: Understanding Dosage and Health Risks

Antihistamines are commonly used medications for treating allergic reactions. They work by blocking the effects of histamine, a chemical that is released by the immune system in response to an allergen. While antihistamines can provide relief from symptoms such as sneezing, itching, and runny nose, exceeding the recommended dosage can lead to serious health risks. In fact, according to a report by the American Association of Poison Control Centers, there were over 25,000 reported cases of antihistamine overdose in the United States in 2019 alone. Therefore, it is important to understand the recommended dosage guidelines for antihistamines, factors affecting dosage, and the potential health risks associated with exceeding those guidelines. In this blog post, we will explore these topics in detail and provide you with the information you need to safely and effectively use antihistamines.

Understanding Antihistamines

What are Antihistamines?

Antihistamines are a type of medication that helps to reduce the effects of histamine in the body. Histamine is a chemical released by the immune system in response to an allergen, such as pollen or pet dander. It causes symptoms such as sneezing, itching, runny nose, and watery eyes.

Antihistamines work by blocking the action of histamine, which in turn reduces the symptoms of allergic reactions. They can be taken orally, as tablets or capsules, or applied topically, as creams or ointments.

There are two types of antihistamines: first-generation and second-generation. First-generation antihistamines have been around for a long time and are available both over-the-counter and by prescription. They tend to cause drowsiness and other side effects, and are not recommended for use during activities that require alertness, such as driving. Second-generation antihistamines are newer medications that are less likely to cause drowsiness and have fewer side effects.

It’s important to note that while antihistamines can be effective at reducing the symptoms of allergies, they do not cure the underlying condition. It’s also important to follow the recommended dosage instructions, as taking too much antihistamine can lead to serious health risks, such as toxicity and organ damage.

Overall, antihistamines can be a helpful tool in managing allergic reactions, but it’s important to talk to your healthcare provider about whether they are right for you and how to use them safely and effectively.

Types of Antihistamines

Types of Antihistamines

Antihistamines are classified into two main types: first-generation and second-generation antihistamines. While both types are effective in treating allergies, they differ in their mechanism of action and side effect profile.

First-Generation Antihistamines

First-generation antihistamines, also known as sedating antihistamines, were the first type of antihistamines to be developed. They work by binding to histamine receptors in the brain and central nervous system, causing drowsiness and other side effects such as dry mouth, blurred vision, and constipation.

Some common examples of first-generation antihistamines include diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), and promethazine (Phenergan). These medications are available in both OTC and prescription forms. However, due to their sedative effects, they are not recommended for use during daytime activities or when driving.

Second-Generation Antihistamines

Second-generation antihistamines, also known as non-sedating antihistamines, were developed to address the side effects associated with first-generation antihistamines. They work by selectively targeting histamine receptors in the periphery, which reduces the risk of drowsiness and other central nervous system side effects.

Some examples of second-generation antihistamines include loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra). These medications are available both OTC and by prescription, and are generally considered safe and effective for most people.

Prescription vs. OTC Antihistamines

While some antihistamines are available over-the-counter (OTC), others require a prescription from a healthcare provider. In general, first-generation antihistamines are more likely to require a prescription due to their sedative effects, while most second-generation antihistamines are available over-the-counter.

It is important to note that all medications, including antihistamines, can have potential side effects and interactions with other medications. It is always best to consult with a healthcare provider before starting any new medication or changing your current regimen.

In conclusion, understanding the different types of antihistamines and their mechanism of action can help you make informed decisions about which medication is right for you. Whether you opt for an OTC or prescription medication, it is important to follow recommended dosages and be aware of potential side effects and interactions.

Recommended Antihistamine Dosage

Standard Dosage Guidelines

Standard Dosage Guidelines

When it comes to taking antihistamines, following the recommended dosage guidelines is crucial for ensuring safety and efficacy. The optimal dosage can vary depending on a number of factors, including age, weight, gender, and health conditions. Here are the standard dosage guidelines for various populations:

Recommended Dose for Adults

For most first-generation antihistamines, the recommended dose for adults is 25-50 mg every four to six hours as needed. For second-generation antihistamines, the recommended dose may be lower, typically ranging from 5 to 10 mg once or twice daily as needed.

Recommended Dose for Children

The appropriate dosage of antihistamines for children depends on their age, weight, and overall health condition. In general, the recommended doses are as follows:

  • Children ages 2 to 5: 1-2.5 mg every 4-6 hours as needed.
  • Children ages 6 to 12: 5-10 mg every 4-6 hours as needed.
  • Children over 12: Same dose as adults.

It’s worth noting that children under the age of two should not take antihistamines without consulting with a pediatrician first.

Recommended Dose for Elderly

Older adults may require lower doses of antihistamines due to changes in metabolism and kidney function that occur with age. Therefore, the recommended dose for elderly individuals is typically lower than that for younger adults. It’s important for older adults to discuss appropriate dosages with their healthcare provider.

Recommended Dose for Pregnant Women

Pregnant women should generally avoid taking any medications during the first trimester unless absolutely necessary. During the second and third trimesters, some antihistamines may be safe to take at the recommended doses. However, it’s important for pregnant women to consult with their healthcare provider before taking any medication.

In addition to following the recommended dosage guidelines, it’s important to pay attention to any potential side effects and seek medical attention if necessary. By taking antihistamines as directed and under the guidance of a healthcare professional, you can effectively manage your allergies or other symptoms while minimizing the risk of adverse effects.

Factors Affecting Antihistamine Dosage

Factors Affecting Antihistamine Dosage

When it comes to taking antihistamines, the recommended dosage can vary depending on several factors. While some people may be able to take the standard dose with no issues, others may need to adjust their dosage based on age, weight, gender, and health conditions.


Age is an important factor to consider when determining the appropriate dosage of antihistamines. Children and elderly individuals may require a different dose than adults. For example, some antihistamines are not recommended for children under a certain age, while others may be safe but require a lower dose. Older adults may also be more susceptible to adverse effects of antihistamines such as drowsiness or confusion, so dosage adjustments may be needed.


Weight is another factor that can affect how much antihistamine a person should take. Generally, those who weigh more may require a higher dose, while those who weigh less may need a lower dose. It’s important to follow the recommended guidelines or consult with a healthcare provider to ensure the proper dosage is being taken.


In general, gender does not have a significant impact on antihistamine dosage. However, there are some exceptions. For instance, some studies suggest that women may be more sensitive to the sedative effects of certain antihistamines, which may require adjusting the dose.

Health Conditions

Certain health conditions can impact how much antihistamine a person should take. For instance, individuals with liver or kidney problems may need to reduce their dose, as these organs are responsible for processing and eliminating medications from the body. Additionally, certain medications or supplements can interact with antihistamines, causing potentially harmful side effects. In some cases, it may be necessary to avoid taking antihistamines altogether if they could exacerbate an underlying health condition.

In conclusion, when taking antihistamines, it’s essential to consider several factors that can impact the recommended dosage. Age, weight, gender, and health conditions can all play a role in determining how much antihistamine is appropriate for an individual. By understanding these factors, individuals can take steps to ensure they are taking the proper amount of medication for their needs.

Exceeding the Recommended Dosage

Health Risks of Overdosing

Overdosing on antihistamines can be extremely dangerous and lead to various health risks. One of the most serious risks of overdosing is toxicity, which occurs when the body is unable to process the excess medication. Toxicity can cause a range of symptoms, including confusion, dizziness, and a rapid or irregular heartbeat.

Another potential risk of antihistamine overdose is organ damage. This can occur when the excess medication causes damage to vital organs such as the liver or kidneys. Symptoms of organ damage may include abdominal pain, fatigue, and dark urine.

In some cases, antihistamine overdose can even result in fatality. This is particularly true if the individual has underlying health conditions or takes other medications that interact with antihistamines. It’s important to seek medical attention immediately if you or someone you know has overdosed on antihistamines.

To prevent these health risks, it’s crucial to follow the recommended dosage guidelines for antihistamines. Taking more than the recommended amount can have serious consequences and should be avoided at all costs. Additionally, individuals should consult with their healthcare provider before taking any new medication to ensure it is safe for them to use.

Overall, understanding the health risks associated with antihistamine overdose can help individuals make informed decisions about their medication use and prioritize their health and well-being.

Symptoms of an Antihistamine Overdose

Symptoms of an Antihistamine Overdose

Antihistamines are medications that are commonly used to treat allergic reactions, but they can be dangerous when taken in excess. An antihistamine overdose occurs when an individual takes more than the recommended amount of the medication. The symptoms of an antihistamine overdose can range from mild to severe and can vary depending on the type and amount of medication taken.

Dizziness and Confusion

One of the most common symptoms of an antihistamine overdose is dizziness and confusion. This is because antihistamines can affect the brain and nervous system, leading to feelings of disorientation and confusion. In some cases, individuals may experience hallucinations or psychosis.

Nausea and Vomiting

Another common symptom of an antihistamine overdose is nausea and vomiting. This occurs because antihistamines can irritate the stomach lining, leading to digestive issues. In severe cases, individuals may experience dehydration and electrolyte imbalances.

Blurred Vision

Antihistamines can also affect vision, leading to blurred or double vision. This occurs because antihistamines can interfere with the eye’s ability to focus properly. In some cases, this can lead to temporary blindness or other vision problems.

Seizures and Unresponsiveness

In rare cases, an antihistamine overdose can lead to seizures and unresponsiveness. This occurs because antihistamines can affect the central nervous system, leading to abnormal electrical activity in the brain. In severe cases, individuals may require emergency medical treatment to prevent permanent damage or death.

It is important to seek medical attention immediately if you suspect that you or someone else has overdosed on antihistamines. Treatment for an antihistamine overdose typically involves supportive care, such as intravenous fluids and medications to control seizures or other symptoms. With prompt treatment, most individuals can recover from an antihistamine overdose without long-term complications.

Treatment for Antihistamine Overdose

Treatment for Antihistamine Overdose

When a person exceeds the recommended dose of antihistamines, they may experience an overdose. In such cases, prompt medical treatment is necessary to prevent severe health complications or even death. The following are some common treatments for antihistamine overdose:

Activated Charcoal

Activated charcoal is a medication that can help absorb any remaining antihistamines in the digestive system before they are absorbed into the bloodstream. It is often given as a form of emergency treatment, especially if the person has ingested the medication within the last hour.


Laxatives can be administered to help eliminate the excess antihistamines from the body. This method can be useful when activated charcoal is not available or when the overdose is less severe.

Gastric Lavage

Gastric lavage, also known as stomach pumping, is a procedure in which a tube is inserted through the mouth into the stomach to remove any contents that may contain antihistamines. This method is usually reserved for severe cases where other methods have failed.

Intravenous Fluids

Intravenous fluids may be given to help flush out the antihistamines from the bloodstream. This method can be particularly helpful when the overdose causes dehydration or electrolyte imbalances.


In some cases, medications may be given to counteract the effects of the antihistamines. For example, if the person is experiencing seizures, an anti-seizure medication may be given to control them.

It is important to seek medical attention immediately if you suspect an antihistamine overdose. Only a healthcare professional can determine the appropriate treatment for the severity of the situation.



In conclusion, antihistamines are effective in treating a range of allergy symptoms, but it’s crucial to follow the recommended dosage guidelines to avoid potential health risks. Taking more than the suggested amount can lead to toxicity, organ damage, and even death in severe cases.

It’s also important to keep in mind that factors such as age, weight, and underlying health conditions can affect how much antihistamine one should take. Pregnant women, for example, may require lower doses than the average adult.

In addition, different types of antihistamines have varying levels of potency and effectiveness. While some first-generation antihistamines may cause drowsiness, second-generation options generally have fewer side effects.

Overall, when using antihistamines, it’s essential to balance their benefits with the potential risks and make informed decisions based on individual needs and circumstances. By doing so, individuals can effectively manage their allergies while minimizing the chances of adverse health outcomes.
Antihistamines can be incredibly effective in managing allergies and other conditions related to histamine release. However, it is crucial to take the recommended dosage and avoid exceeding it, as doing so can result in severe health risks and potentially even fatal outcomes. It is important to consult with a healthcare provider before taking any antihistamines, particularly if you have underlying health conditions or are taking other medications. By following the recommended dosage guidelines and understanding the risks associated with exceeding them, you can safely and effectively use antihistamines to manage your symptoms and improve your quality of life.

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