Antihistamines

What are antihistamines?

Antihistamines are a type of medication commonly used to treat allergy symptoms. They work by blocking the action of histamine, a substance released by the immune system when it detects allergens. Histamine is responsible for many common allergic reactions, such as itching, sneezing, runny noses, and hives. By preventing histamine from binding to its receptors in the body, antihistamines can reduce or eliminate these symptoms.

These medications are most often used to manage conditions like hay fever, seasonal allergies, food allergies, and hives. Some antihistamines can also help treat cold symptoms or motion sickness, as they may reduce sneezing, congestion, or nausea. Antihistamines come in various forms, such as tablets, liquids, nasal sprays, and eye drops.

There are two main types of antihistamines. First-generation antihistamines, like diphenhydramine and chlorpheniramine, are known for causing drowsiness because they can cross the blood-brain barrier and affect the central nervous system. Second-generation antihistamines, such as loratadine, cetirizine, and fexofenadine, are less likely to cause drowsiness, making them a better option for daytime use. While antihistamines are generally effective, it's important to use them properly and follow the dosage instructions. It's also wise to check for potential interactions with other medications you may be taking, as well as any side effects that might occur.

How long do antihistamines take to work?

Antihistamines typically begin to work within 30 minutes to an hour after taking them, though this can vary depending on the specific type of antihistamine. Some may start providing relief more quickly, while others may take longer. First-generation antihistamines (like diphenhydramine) may act faster but can also cause drowsiness. Second-generation antihistamines (like loratadine or cetirizine) may take a little longer to start working but generally cause fewer side effects like drowsiness and are more suitable for daytime use.

The full effect of the medication, such as complete relief from symptoms like sneezing, itching, or congestion, can take a bit longer, and you might need to take the antihistamine consistently for a few days to experience its full benefit for chronic conditions like hay fever. Always follow the recommended dosage instructions for the best results, and consult a healthcare provider if you don't experience relief.

Can you take antihistamines when pregnant?
Some antihistamines are considered safe to take during pregnancy, but it’s important to consult with a healthcare provider before using them. Generally, second-generation antihistamines like loratadine (Claritin) and cetirizine (Zyrtec) are considered safer options for use during pregnancy because they are less likely to cause drowsiness and are less likely to pass into the placenta compared to first-generation antihistamines like diphenhydramine (Benadryl), which may have more sedative effects.

While these medications are usually regarded as safe for short-term use during pregnancy, it's still important to talk to a doctor or midwife to ensure that it's the right choice for your individual health and circumstances. In some cases, they may recommend non-medication approaches for managing allergies during pregnancy, such as nasal saline sprays or other natural remedies.
 

Can an antihistamine help a cold?

Antihistamines can provide some relief from certain cold symptoms, but they don’t directly treat the underlying viral infection. When you have a cold, your body releases histamine as part of the immune response, which can contribute to symptoms like runny nose, sneezing, and congestion. Antihistamines work by blocking the effects of histamine, which can help reduce these symptoms, particularly the nasal congestion and sneezing associated with a cold.

However, antihistamines are generally more effective for allergic reactions (like hay fever) than for viral infections like the common cold. First-generation antihistamines (like diphenhydramine) may also make you feel drowsy, which can be helpful if you need rest, but they are not a cure for a cold.

For a cold, decongestants, pain relievers, and hydration are typically more helpful in managing symptoms. If you're unsure about which treatment is best for your symptoms, it’s a good idea to consult with a healthcare provider.
 

Can you take antihistamines with paracetamol?
In most cases, it is generally safe to take antihistamines with paracetamol (acetaminophen) because they work in different ways and do not typically interact with each other. Antihistamines help alleviate allergy symptoms by blocking the effects of histamine, while paracetamol is a pain reliever and fever reducer.

However, it’s important to follow the recommended dosage for both medications and not exceed the maximum daily limits. If you’re using a combination medication (such as cold or flu medicines), it’s essential to check the ingredients to ensure you're not accidentally doubling up on any active ingredients, such as a second antihistamine or pain reliever.

If you have any specific health concerns, such as liver problems or are taking other medications, it's always a good idea to consult with a healthcare provider or pharmacist before combining medications.

Do antihistamines make you sleepy?
Yes, certain antihistamines can make you feel sleepy, particularly first-generation antihistamines such as diphenhydramine (Benadryl) and chlorpheniramine. These older antihistamines can cross the blood-brain barrier, which can cause drowsiness as a side effect. This sedative effect is one reason why some people use them to help with sleep.

However, second-generation antihistamines, such as loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra), are designed to be non-drowsy and cause far less sedation. These are typically preferred for daytime use, as they relieve allergy symptoms without making you feel sleepy.

If you're concerned about feeling drowsy, it's best to choose a second-generation antihistamine, but if you need help sleeping, a first-generation antihistamine may be useful. Always check with a healthcare provider if you're unsure about which antihistamine is best for your needs.