Decongestants vs. Antihistamines

Decongestants and antihistamines are commonly used to help relieve nasal congestion (stuffy nose), sneezing, and runny nose usually caused by common colds and allergies. Antihistamines often make people drowsy, while decongestants can cause insomnia due to one of its active ingredients called pseudoephedrine^[¹^]. Both are available as over-the-counter or prescription drugs, and here’s everything you should know before taking a decongestant or an antihistamine.

What are the main differences between decongestants and antihistamines?

Understanding your symptoms and being able to distinguish between a cold or allergies can help you decide which medication is right for you.

Decongestants tend to be more appropriate for treating a cold because they help reduce swelling in the nasal passageways caused by inflammation from an infection. This will help you breathe easier by reducing built-up pressure, therefore improving airflow through the nose. Not only will they relieve your stuffy nose, but can also help reduce ear congestion symptoms.

Antihistamines, on the other hand, are a class of drugs that block a chemical called histamine that is released by the immune system during allergic reactions. They help relieve allergy symptoms such as watery eyes, runny nose, swelling, and hives. Antihistamines typically make you drowsy but there are also non-drowsy options that interfere less with everyday life.

What is histamine?

Histamines are chemicals made by your immune system that help your body get rid of an unwanted substance —allergies or an allergen. When a person is allergic to something, such as a type of food or dust, the immune system mistakenly believes that this usually harmless substance is actually harmful to the body. In an attempt to protect itself, the immune system starts a chain reaction that prompts the body to release histamine, along with other chemicals into the bloodstream. The histamine then acts on a person's eyes, nose, throat, lungs, skin, or gastrointestinal tract, causing allergy symptoms. In this case, you would take an antihistamine to help fight symptoms caused by the release of histamine during an allergic reaction^[²^]. Too much histamine produced by your body from being oversensitive and overreacting to an allergen can cause a variety of symptoms, including:

Congestion, coughing
Wheezing, shortness of breath
Tiredness and fatigue
Itchy skin, hives, and other skin rashes
Itchy, red, watering eyes
A running or blocked nose, or sneezing
Insomnia
Nausea and vomiting

Antihistamines

First-Generation Antihistamines:

These are the first-generation antihistamines developed by scientists and often have sedating side effects. They should be taken with caution when driving or performing activities that require alertness. Some common over-the-counter and prescription antihistamines include^[³^]:

Brompheniramine (Children’s Dimetapp Cold^®)
Chlorpheniramine (Chlor-Trimeton^®)
Diphenhydramine (Benadryl^®)
Doxylamine (Vicks NyQuil®, Tylenol Cold)
Clemastine (Dayhist^®)
Cyproheptadine (Periactin^®)
Dexchlorpheniramine
Dimenhydrinate (Dramamine^®)
Hydroxyzine (Vistaril^®)
Phenindamine (Nolahist^®)

Second-Generation Antihistamines:

These are newer medicines and many treat allergy symptoms without causing as much drowsiness. Commonly used over-the-counter products include:

Antihistamine Nasal Spray:

Antihistamine nasal sprays can help relieve sneezing, itchy or runny nose, sinus congestion, and postnasal drip. Side effects of antihistamine nasal sprays might include bitter taste, drowsiness, or feeling tired. Prescription antihistamine nasal sprays include:

Azelastine (Astelin, Astepro)
Olopatadine (Patanase)

Antihistamine Eye Drops:

Antihistamine eye drops, available over-the-counter or by prescription, can help ease itchy, red, swollen eyes. Side effects might include headaches and dry eyes. If antihistamine eye drops sting or burn, try keeping them in the refrigerator for soothing effects. Instilling refrigerated artificial tear drops prior to antihistamine eye drops may alleviate some of the burning sensation^[¹^]. Some examples include:

Ketotifen (Alaway, Zaditor)
Olopatadine (Pataday, Patanol, Pazeo)
Pheniramine and naphazoline (Visine, Opcon-A)

Common Side Effects of Antihistamines

Consult your doctor or pharmacist prior to taking any antihistamines. Some common side effects of first-generation antihistamines include:

Drowsiness
Dry mouth, dry eyes
Blurred or double vision
Dizziness and headache
Low blood pressure
Mucus thickening in the airways
Rapid heart rate
Difficulty urinating and constipation

Note that even though these symptoms are more profound and distinct with first-generation antihistamines, they still can be caused by second-generation antihistamines, just to a much lesser extent.

Antihistamine Drug Interactions

Antihistamines can interact with other medicines you take—especially if you take more than one medication, so it’s important to know each active ingredient. Talk to your doctor before taking a first-generation antihistamine if you take any medicines that can make you feel drowsy. These include sleeping pills, sedatives, antioxylitics, and muscle relaxants. Antihistamines are often combined with decongestants and/or pain relievers.

Are antihistamines safe to take during pregnancy/breastfeeding?

During pregnancy, up to 10% to 30% of women with pre-existing allergic rhinitis have reported increased symptoms. Therefore, short-term or occasional use of the older generation antihistamines would not be expected to be a concern during breastfeeding^[⁵^]. Talk to your OBGYN before taking any medications, prescribed or over-the-counter.

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Decongestants

When should I use a decongestant?

Decongestants are used for quick, temporary relief of nasal and sinus congestion commonly caused by the common cold, flu, allergies, or other breathing illnesses (such as sinusitis and bronchitis). They can cause trouble sleeping, headache, increased blood pressure, and irritability. Decongestants with pseudoephedrine as the active ingredient are not recommended for people with high blood pressure, cardiovascular disease, glaucoma, hyperthyroidism, and several other medical conditions^[¹^].
Decongestants come in the form of pills, liquids, nasal drops, and sprays and many are available without a prescription. Common decongestant drugs include:

Afrin, Dristan, Vicks Sinex (oxymetazoline)
Sudafed PE, Suphedrin PE (phenylephrine)
Silfedrine, Sudafed, Suphedrin (pseudoephedrine)

Ask your doctor for medical advice before taking decongestants if you have the following health issues:

Glaucoma
High blood pressure
Heart conditions
Thyroid problems
Enlarged prostate
Diabetes

Common Side Effects of Decongestants

Side effects of decongestants include:

Burning, stinging, dryness, and local irritation of the nose (for nasal drops and spray)
Sneezing
Rebound congestion (Rhinitis medicamentosa)
High blood pressure
Fast heartbeat
Seizures
Anxiety
Dizziness
Tremors

Decongestants can cause a jittery feeling or trouble sleeping. If that happens, cut back on caffeine while taking them. If that doesn't help, you may need to stop taking them. Compared to oral products, nasal sprays are less likely to cause these systemic problems, so they can be used as a short-term solution.

Are decongestants safe to take during pregnancy/breastfeeding?

Over-the-counter decongestants are, for the most part, safe during pregnancy, physicians advise. Pseudoephedrine and phenylephrine are available over the counter as Sudafed and are safe for many women to use during pregnancy^[⁶^]. Be aware of combination decongestant products that contain acetaminophen (Tylenol), using more than the daily recommended dose of acetaminophen can lead to liver injury.

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