Why Does Antihistamines/Paracetamol Cause Sleepiness

Histamine is a chemical that our immune system release. It’s produced by the white blood cells when experiencing allergy and signal the body to fight off invaders.

There are mast cells who act as a sentinels, detecting the presence of parasites and other possible dangers in surrounding cells and tissues. And there is basophils (leukocyte), a type of white blood cell that helps our body from allergens and parasites.

When our body encounter an invader, histamines are released. The surrounding blood vessels will become leakier to give the ring to white blood cells to fight the invaders. The leakier blood vessels and increased inflammation lead to allergy symptomps you experience such as:

• Runny nose
• Sore throat
• Red skin rash
• Vomiting
• Diarrhea
• Itchy nose

And antihistamines role is to soothe the symptoms of allergy reactions by slowing down the histamine action. In allergy drugs, often times it comes with paracetamol, that calms your body when your body is fighting the invaders (pain relief). Antihistamines make you sleepy because they block the histamine signals that keep your brain alert.

Paracetamol and antihistamines itself does not cure the underlying cause of the allergy, they only manage the symptoms (runny nose, headache, etc). Drugs usually come with the most important chemical along with paracetamol or antihistamines depending on the symptoms you experience. For example, guaifenesin is for wet cough, pseudophedrine for runny nose or flu.