Highly sedative antihistamines are primarily first-generation (older) types that cross the blood-brain barrier, including Diphenhydramine (Benadryl), Promethazine (Phenergan), Chlorphenamine (Piriton), Doxylamine, Alimemazine, and Hydroxyzine, known for causing significant drowsiness, making them useful for sleep but also risky for driving or operating machinery.
Conclusions: Diphenhydramine is known for its sedative properties and is often used in studies as positive control. Diphenhydramine has been shown to consistently impair objective and subjective measures of CNS performance at single doses as low as 25mg.
Types of antihistamine
Combining this medication with alcohol or other depressants (including antihistamines, narcotics and some dental anesthetics) can make side effects more severe.
Diphenhydramine is one of the most widely available, longest-used antihistamine medications but has many side effects including sedation and risk of toxicity in overdose including cardiac toxicity.
Some antihistamine medicines available without a prescription can make you drowsy. But they aren't meant for ongoing sleep problems. That condition is called chronic insomnia.
Side effects include drowsiness, so use with caution if you need to drive or be alert. Antihistamines that tend to cause drowsiness include: Diphenhydramine.
You generally cannot take antihistamines with substances that cause drowsiness (alcohol, opioids, sedatives) or other anticholinergic drugs (certain antidepressants, bladder meds, some cold meds) due to increased side effects like extreme sleepiness, confusion, or breathing problems; also, avoid mixing with MAO inhibitors and certain antifungals/antibiotics without doctor approval, as these can cause serious reactions. Always check with a doctor or pharmacist about potential interactions before combining antihistamines with other medications, notes Patient.info, HSE website, and FamilyDoctor.org.
Taking opioid-based medicines, like codeine, morphine or oxycodone, together with amitriptyline can increase your risk of becoming very drowsy and having breathing problems. Tell your doctor if you've ever taken any medicines for depression.
The "best" antihistamine depends on your needs (e.g., non-drowsy vs. strong relief), but popular, effective over-the-counter choices for general allergies include Cetirizine (Zyrtec), Loratadine (Claritin), and Fexofenadine (Allegra), offering 24-hour, less-sedating relief, with Levocetirizine (Xyzal) often cited for higher potency. For severe symptoms, prescription options might be needed, while older ones like Diphenhydramine (Benadryl) offer quick relief but cause drowsiness. Always consult a doctor or pharmacist to find the right fit for you, especially if pregnant or breastfeeding.
Hydroxyzine is used to help control anxiety and tension caused by nervous and emotional conditions. It can also be used to help control anxiety and produce sleep before surgery. This medicine is also used to relieve symptoms of allergic conditions (eg, chronic urticaria and atopic and contact dermatoses).
Cetirizine tends to start relieving allergy symptoms faster, usually within 30-60 minutes. However, it also has a higher risk of causing drowsiness as a side effect. Loratadine takes a bit longer to start working, around 1-3 hours but is less likely to make you feel sedated during the day.
Doxylamine and other first-generation antihistamines are the most widely used sleep medications in the world. Typical side effects of doxylamine include dizziness, drowsiness, grogginess, and dry mouth, among others.
Sedating antihistamines that are available from pharmacies for allergies include:
Promethazine is an antihistamine sometimes used as a sleeping pill. It's also known by the trade name Phenergan. Promethazine is an ingredient in some over-the-counter cold and flu medicines, such as Night Nurse.
Cetirizine is more likely to cause drowsiness and should not be taken with theophylline or other substances that may cause drowsiness.
Amitriptyline is not suitable for some people. To make sure it's safe for you, tell your doctor if you: have ever had an allergic reaction to amitriptyline or any other medicine. have a heart problem – amitriptyline can make some heart problems worse.
This is because it can make you feel sleepy. If you find that you're still feeling sleepy when you wake up in the morning, you could try taking it earlier in the evening. Amitriptyline doesn't usually upset the stomach, so you can take it with or without food.
Amitriptyline is used at higher doses for the treatment of depression and low mood (50mg-200mg per day) and at lower doses to treat pain and prevent migraines (10-75mg per day). The dosage of amitripyline for insomnia treatment is at the lowest end of the scale, typically within the range of 10-25mg per day.
Diphenhydramine is a first-generation antihistamine that can cause significant drowsiness, making it useful as a sleep aid for people 12 years and older.
People with conditions like glaucoma, enlarged prostate, heart disease, high blood pressure, asthma, liver or kidney disease, epilepsy, overactive thyroid, diabetes, or those who are pregnant/breastfeeding, or giving them to young children (under 2-6 years), should avoid or be cautious with antihistamines, especially older, sedating types, and should consult a doctor or pharmacist first due to risks like worsening urinary retention, glaucoma, or causing serious harm in kids.
antihistamines that make you feel drowsy (sleepy) – like chlorphenamine (Piriton), cinnarizine, diphenydramine, hydroxyzine and promethazine. non-drowsy antihistamines that are less likely to make you feel sleepy – like acrivastine, cetirizine, fexofenadine and loratadine.
Synopsis: Sedation results in slower reaction times and impaired performance in activities that require diligent attention. Drowsiness is the subjective feeling of being tired. The two are not always connected; sedation can occur without drowsiness, and vice versa.
First-generation antihistamines more easily cross your blood-brain barrier into your central nervous system. This causes drowsiness. Second-generation antihistamines are generally safer because they don't cause drowsiness and interact with fewer medications.
If your allergy medication isn't working or you have new allergy symptoms, it may be time to visit your healthcare professional for an updated round of allergy tests. If you have new allergies, you may need to change your medications. You may also need a plan to avoid new triggers.