Useful information

Cold medicine – why does it make you sleepy?


This winter, the number of influenza cases has decreased sharply compared to the average
year, probably because of the influence of the new coronavirus, or because of everyone’s high
awareness of prevention. According to the Ministry of Health, Labor and Welfare, the number of
patients reported by about 5,000 medical institutions nationwide in the week ending December
20, 2020 is 1/1500 of the same period of the previous year.
However, as the temperature drops and the air dries, many people get so-called colds such as
nasal colds and throat colds. This time, we will talk about cold medicine (common cold
medicine) and drowsiness.

What is “common treatment”?

Many people buy a common cold OTC (over-the-counter) medicine at a pharmacy or drugstore
when they catch a cold or at the beginning of a cold.
A common cold medicine is a medicine that contains various ingredients to relieve various
symptoms caused by so-called colds (fever, headache, sore throat, cough, sneezing, runny
nose, stuffy nose, etc.). That is why it is a “common” treatment.

What is an “antihistamine”?

By the way, taking a common cold medicine (cold medicine) may make you sleepy. The main
cause is “antihistamines”.
Antihistamine medications are formulated to control symptoms such as runny nose, stuffy nose,
and sneezing. Ingredient names (generic names) include “chlorpheniramine maleate,”
“diphenhydramine hydrochloride,” and “clemastine fumarate,” which are antihistamines.
When the substance that causes an allergic reaction enters the nose, “histamine” is produced in
the mucous membrane of the nose, and it sticks to the “receptor,” also in the mucous
membrane of the nose, causing allergic symptoms such as sneezing and runny nose.
Therefore, antihistamines suppress allergic symptoms such as runny nose, stuffy nose, and
sneezing by blocking the receptors so that the histamine and the receptors don’t stick to each
other, even if histamine is produced.

Why cold medicine causes drowsiness

While it has the effect of suppressing unpleasant symptoms such as runny nose, stuffy nose,
and sneezing, antihistamines are known to have side effects such as drowsiness and poor
The reason they have these side effects is that the substance histamine not only causes allergic
symptoms on the mucous membrane of the nose, but also has the effect of stimulating the
brain. Therefore, when an antihistamine enters the brain, it suppresses the histamine effect of
stimulating the brain, which makes you sleepy or hazy. This slowing down of brain activity by
antihistamines is called “dull brain”.

How to choose a medicine that doesn’t make you sleepy

If you take a cold medicine to control your symptoms and feel refreshed, but you still feel sick, it
may be because of this dull brain. By the way, it is the activity of the medicine that suppresses
runny nose and stuffy nose and causes drowsiness. Just because it causes drowsiness does
not mean that it has a strong effect – but that’s another story.
Of course, when using medicine, it is better to have few side effects.
Common cold medicine is easy and quick to use for dealing with various symptoms with a single
medication, but in order to reduce side effects, it is better for it to contain only the ingredients
necessary to relieve the troublesome symptoms. It is also important to choose the right one. If
you don’t know what medicine to choose, talk to your pharmacist.