Antihistamines are a widely used class of medications primarily known for treating allergy symptoms such as sneezing, itching, watery eyes, and hives. They work by blocking the effects of histamine, a chemical the immune system releases during an allergic reaction. These medications are available over-the-counter and by prescription, and are also found in various cold and flu remedies. While generally considered safe and effective for their intended purposes, a common question arises regarding their potential to cause anxiety as a side effect.
Do Antihistamines Cause Anxiety?
Antihistamines are categorized into different generations based on their chemical properties and effects on the body. First-generation antihistamines, such as diphenhydramine (Benadryl), hydroxyzine (Vistarax, Atarax), and chlorpheniramine, are more likely to cause central nervous system (CNS) side effects. These medications can induce drowsiness, but in some individuals, they may paradoxically lead to agitation, restlessness, or anxiety. This “paradoxical excitation” is a recognized potential side effect, particularly in children.
In contrast, second-generation antihistamines, including loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra), are generally less likely to cause such CNS effects. These newer antihistamines are designed to have less impact on the brain, reducing the likelihood of drowsiness and other neurological side effects. Hydroxyzine, a first-generation antihistamine, is notable as it is FDA-approved for the short-term treatment of anxiety due to its calming effects, yet it can still cause agitation in some cases.
How Antihistamines Can Influence Anxiety
The way certain antihistamines can contribute to anxiety relates to their interaction with the central nervous system. First-generation antihistamines readily cross the blood-brain barrier, which is a protective filter between the bloodstream and the brain. Once inside the brain, they block histamine H1 receptors, which are involved in regulating wakefulness, attention, and other brain functions. This widespread effect on brain histamine can lead to sedation for many users.
Beyond blocking histamine, these older antihistamines also have anticholinergic effects, meaning they block the action of acetylcholine, another important neurotransmitter. Acetylcholine plays a crucial role in memory, learning, and overall brain activity. The disruption of these various neurotransmitter systems can lead to a range of CNS effects, including confusion, dizziness, and, in some susceptible individuals, a paradoxical stimulation that manifests as nervousness, agitation, or anxiety.
Addressing Antihistamine-Related Anxiety
For individuals who suspect their antihistamine medication is contributing to feelings of anxiety, consulting a healthcare professional is an important first step. It is not advisable to make changes to medication without medical guidance. A doctor or pharmacist can help review the current type and dosage of antihistamine being used.
One common recommendation might be to consider switching from a first-generation antihistamine to a second-generation alternative. Second-generation antihistamines are designed to have a reduced impact on the central nervous system, making them less likely to cause anxiety or other CNS side effects. Monitoring symptoms by keeping a log of medication use and how symptoms of anxiety fluctuate can provide valuable information for a healthcare provider to identify patterns and adjust treatment effectively.