“DM medicine” typically refers to over-the-counter cough and cold medications that contain dextromethorphan. Drowsiness is a common and expected side effect when taking these medications. Understanding the active ingredients in these remedies helps explain why sleepiness occurs.
How Dextromethorphan Causes Drowsiness
Dextromethorphan (DM) functions as a cough suppressant by affecting the central nervous system, specifically the brain’s cough center. While its primary role is to calm the cough reflex, it also interacts with various neurotransmitter systems in the brain, contributing to its potential for causing drowsiness.
DM acts as a low-affinity antagonist at N-methyl-D-aspartate (NMDA) receptors. These receptors are involved in neuronal transmission, and blocking them can lead to a reduction in brain activity. Additionally, dextromethorphan inhibits the reuptake of serotonin, a neurotransmitter that plays a role in mood and sleep. These combined effects on brain chemistry can result in central nervous system depression, leading to feelings of sleepiness and sedation.
Other Common Ingredients and Their Sedating Effects
Many “DM medicine” products are combination medications, containing more than just dextromethorphan. Other active ingredients commonly found in these remedies can significantly contribute to drowsiness. First-generation antihistamines are frequent additions due to their ability to relieve symptoms like runny nose, sneezing, and watery eyes.
Antihistamines such as diphenhydramine and chlorpheniramine work by blocking histamine H1 receptors. While histamine is involved in allergic responses, it also plays a role in regulating wakefulness in the brain. Because these first-generation antihistamines can cross the blood-brain barrier, they interfere with histamine’s wakefulness-promoting signals, leading to sedation and drowsiness. This is why many nighttime cold formulas specifically include these types of antihistamines.
Safe Use and Managing Drowsiness
When taking DM medicine, it is important to be aware of the potential for drowsiness and take precautions. Individuals should avoid activities requiring full mental alertness, such as driving or operating heavy machinery, until they understand how the medication affects them. Alcohol consumption should also be avoided, as it can intensify the nervous system side effects of dextromethorphan and other sedating ingredients, increasing drowsiness and impairing judgment.
To minimize daytime drowsiness, it can be beneficial to take these medications at night, especially those formulated for nighttime use. Always read the product label carefully to understand the active ingredients and follow the recommended dosage instructions. If drowsiness is severe or persistent, or if there are concerns about interactions with other medications, consulting a healthcare professional is advisable.