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What Does Diphenhydramine Syrup Do? Uses, Side Effects, and Safety

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9 min read

Discovered in 1943, the active ingredient in diphenhydramine syrup is a first-generation antihistamine known for its sedative properties. What does diphenhydramine Syrup do? It works by blocking histamine to effectively treat allergy symptoms, motion sickness, and occasional sleeplessness.

Quick Summary

Diphenhydramine syrup is a first-generation antihistamine that provides temporary relief for allergies, motion sickness, and insomnia, but causes significant drowsiness and requires careful consideration before use.

Key Points

  • Primary Action: Diphenhydramine syrup is a first-generation antihistamine that blocks histamine to relieve common allergy and cold symptoms like sneezing and a runny nose.

  • Effective Sleep Aid: Its sedative side effects, caused by crossing the blood-brain barrier, make it effective as an occasional sleep aid for adults.

  • Motion Sickness Prevention: The syrup is also used to prevent and treat motion sickness, with the first use recommended 30 minutes before travel.

  • Important Side Effects: Common side effects include drowsiness, dry mouth, dizziness, and constipation; children may experience paradoxical excitation.

  • Safety Precautions: Use is not recommended for infants or older adults without medical guidance due to heightened risks, and it should not be combined with alcohol or other sedating drugs.

In This Article

How Diphenhydramine Syrup Works

Diphenhydramine is a first-generation antihistamine that acts as an inverse agonist at the histamine H1 receptor. During an allergic reaction, the body releases histamine, which causes symptoms like sneezing, itching, and watery eyes. By blocking the H1 receptors, diphenhydramine prevents histamine from binding and reduces these allergic responses.

Unlike newer, second-generation antihistamines, diphenhydramine readily crosses the blood-brain barrier. This allows it to act on H1 receptors in the central nervous system (CNS), which is what causes its most well-known side effect: drowsiness. This CNS effect is responsible for its use as a sleep aid. The medication also has anticholinergic properties, blocking muscarinic acetylcholine receptors, which can lead to side effects such as dry mouth and blurred vision.

Common Uses for Diphenhydramine Syrup

Diphenhydramine syrup has a variety of uses, primarily leveraging its antihistamine and sedative effects.

Allergy and Cold Symptom Relief

For many, diphenhydramine is a go-to for temporary relief of seasonal allergy symptoms caused by hay fever and other upper respiratory allergies. It effectively addresses symptoms such as:

  • Sneezing
  • Runny nose
  • Itchy, watery eyes
  • Itching of the nose or throat

It can also help with cold symptoms like a runny nose and sneezing. However, newer, non-drowsy antihistamines are often preferred for daytime allergy management.

Occasional Insomnia (Sleep Aid)

Due to its ability to cause drowsiness, diphenhydramine is widely used as a nighttime sleep aid for occasional sleeplessness. It is important to note that it is only recommended for short-term use (no more than 7-10 nights), as tolerance to the sedative effect can develop quickly. Health professionals caution against using it for chronic insomnia, which may require a different approach.

Preventing and Treating Motion Sickness

Diphenhydramine is effective in preventing and treating the nausea, vomiting, and vertigo associated with motion sickness. For prevention, it is generally recommended to be taken about 30 minutes before exposure to motion. Its effect on the vestibular system helps to calm the signals that cause motion-related nausea.

Other Uses

While less common, diphenhydramine has been historically used for other conditions, such as treating certain symptoms of Parkinson's disease due to its anticholinergic properties.

Diphenhydramine Syrup vs. Second-Generation Antihistamines

The most notable difference between first-generation antihistamines like diphenhydramine and newer, second-generation alternatives is their effect on the central nervous system. Second-generation antihistamines are often preferred for daily allergy relief because they cause less drowsiness.

Feature Diphenhydramine (Benadryl) Loratadine (Claritin) Cetirizine (Zyrtec)
Generation First-Generation Second-Generation Second-Generation
Sedation Causes significant drowsiness Less likely to cause drowsiness Less likely to cause drowsiness, but possible
Frequency of Use Can be used several times a day as needed Typically used once daily Typically used once daily
Onset of Action Fast-acting (within 30 mins) Slower onset (~2 hours) Quicker onset than Claritin
Primary Use Allergic reactions, sleep aid, motion sickness Seasonal allergies, hives Allergies, hives
Suitability for Elderly Generally avoided due to anticholinergic effects and fall risk Generally safer, but consult doctor A safer option than Benadryl

Important Side Effects

While generally safe when used as directed, diphenhydramine syrup has several potential side effects that users should be aware of.

Common Side Effects:

  • Drowsiness, dizziness, and impaired coordination
  • Dry mouth, nose, and throat
  • Constipation and stomach upset
  • Thickened bronchial secretions
  • Excitability, particularly in children (known as paradoxical excitation)

Serious Side Effects:

  • Vision problems, including blurred vision and seeing halos
  • Difficulty or painful urination
  • Fast or irregular heartbeat
  • Seizures, particularly in children or with overdose
  • Anaphylactic reaction (rare)

Guidelines for Use

It is crucial to follow the instructions provided on the product label or by a healthcare professional. Always use the measuring device that comes with the product to ensure accurate administration. The concentration of the syrup is an important factor in determining the correct amount to use.

Warnings and Precautions

  • Children and Infants: The FDA has warned against using cough and cold products containing diphenhydramine in children under 2 years of age due to risk of serious side effects, and it should not be used to make a child sleepy. Use in children 2 to 5 years old should be under a doctor's guidance.
  • Older Adults: Diphenhydramine is generally not recommended for those 65 and older, except for serious allergic reactions, due to a higher risk of side effects like confusion, dizziness, and falls.
  • Pregnancy and Breastfeeding: Consult a doctor if pregnant or planning to become pregnant. It can pass into breast milk and is not recommended for breastfeeding mothers as it may cause issues for the infant or reduce milk supply.
  • Driving and Machinery: The sedative effect means you should not drive or operate heavy machinery until you know how the medication affects you.
  • Alcohol and Other Medications: Avoid alcoholic beverages, as they can significantly increase drowsiness. Combining with other sedatives, tranquilizers, or antihistamines can also be dangerous.
  • Pre-existing Conditions: Individuals with conditions like glaucoma, enlarged prostate, urinary retention, heart disease, or breathing problems (e.g., asthma, emphysema) should consult a doctor before use.

Conclusion

Diphenhydramine syrup is a versatile over-the-counter medication with a long history of use for relieving allergy symptoms, preventing motion sickness, and providing temporary sleep aid. Its mechanism as a first-generation antihistamine, which blocks histamine receptors both peripherally and in the brain, accounts for its effectiveness but also its significant sedative side effects. While it offers rapid relief, it is not suitable for everyone, particularly young children and older adults. Always follow the instructions for use, utilize a proper measuring device, and consult with a healthcare professional to ensure it is the right and safest choice for your needs, especially if you have pre-existing health conditions or take other medications.

Keypoints

  • Primary Action: Diphenhydramine syrup is a first-generation antihistamine that blocks histamine to relieve common allergy and cold symptoms like sneezing and a runny nose.
  • Effective Sleep Aid: Its sedative side effects, caused by crossing the blood-brain barrier, make it effective as an occasional sleep aid for adults.
  • Motion Sickness Prevention: The syrup is also used to prevent and treat motion sickness, with the first dose recommended 30 minutes before travel.
  • Important Side Effects: Common side effects include drowsiness, dry mouth, dizziness, and constipation; children may experience paradoxical excitation.
  • Safety Precautions: Use is not recommended for infants or older adults without medical guidance due to heightened risks, and it should not be combined with alcohol or other sedating drugs.

Faqs

{ "question": "Is diphenhydramine syrup safe for children?", "answer": "Diphenhydramine syrup is not recommended for children under 2 years of age and should not be used to make any child sleepy. For children ages 6 to 11, use with caution, and always follow specific pediatric instructions after consulting with a doctor." }, { "question": "Can I take diphenhydramine syrup every night for sleep?", "answer": "No, diphenhydramine is only for occasional sleeplessness and should not be used for more than 7-10 consecutive nights. Consistent use can lead to tolerance, and the American Academy of Sleep Medicine does not recommend it for chronic insomnia." }, { "question": "How long does it take for diphenhydramine syrup to work?", "answer": "Oral diphenhydramine starts to work within 30 minutes after taking it, with its peak effects occurring in about 1 to 2 hours." }, { "question": "What are the main side effects of diphenhydramine syrup?", "answer": "The most common side effects are drowsiness, dizziness, dry mouth/nose/throat, and constipation. In children, it can sometimes cause excitability or restlessness." }, { "question": "How does diphenhydramine syrup compare to 'non-drowsy' antihistamines?", "answer": "Diphenhydramine is a first-generation antihistamine that causes significant drowsiness because it crosses the blood-brain barrier. Second-generation antihistamines, like loratadine (Claritin), are less likely to cause drowsiness, making them a better choice for daytime use." }, { "question": "Can I drink alcohol while taking diphenhydramine syrup?", "answer": "No, you should avoid drinking alcohol while taking diphenhydramine syrup. Alcohol can significantly increase the sedating effects of the medication, leading to extreme drowsiness and potential safety risks." }, { "question": "What should I do if I forget to use diphenhydramine syrup as directed?", "answer": "If you are using the medication on a schedule, use the missed amount as soon as you remember. However, if it is almost time for your next scheduled use, skip the missed one. Do not use a double amount to catch up." }

Citations

Disclaimer: Information provided is for general knowledge and is not a substitute for professional medical advice. Always consult a healthcare provider for any health concerns or before making any decisions related to your health or treatment.

Frequently Asked Questions

Diphenhydramine syrup is not recommended for children under 2 years of age and should not be used to make any child sleepy. For children ages 6 to 11, use with caution, and always follow specific pediatric instructions after consulting with a doctor.

No, diphenhydramine is only for occasional sleeplessness and should not be used for more than 7-10 consecutive nights. Consistent use can lead to tolerance, and the American Academy of Sleep Medicine does not recommend it for chronic insomnia.

Oral diphenhydramine starts to work within 30 minutes after taking it, with its peak effects occurring in about 1 to 2 hours.

The most common side effects are drowsiness, dizziness, dry mouth/nose/throat, and constipation. In children, it can sometimes cause excitability or restlessness.

Diphenhydramine is a first-generation antihistamine that causes significant drowsiness because it crosses the blood-brain barrier. Second-generation antihistamines, like loratadine (Claritin), are less likely to cause drowsiness, making them a better choice for daytime use.

No, you should avoid drinking alcohol while taking diphenhydramine syrup. Alcohol can significantly increase the sedating effects of the medication, leading to extreme drowsiness and potential safety risks.

If you are using the medication on a schedule, use the missed amount as soon as you remember. However, if it is almost time for your next scheduled use, skip the missed one. Do not use a double amount to catch up.

References

  1. 1
    Diphenhydramine: MedlinePlus Drug Information
  2. 2
    Diphenhydramine
  3. 3
    Diphenhydramine Uses, Dosage & Side Effects
  4. 4
    Diphenhydramine Oral
  5. 5
    Benadryl vs. Claritin for Allergic Rhinitis
  6. 6
    Benadryl vs. Zyrtec: Uses, Side Effects, and Benefits
  7. 7
    Using Benadryl to Sleep? It's Not Always a Good Idea
  8. 8
    FDA warns about serious problems with high doses of the allergy medicine diphenhydramine (Benadryl)
  9. 9
    Medications That Should Never Be Combined with Benadryl
  10. 10
    Benadryl (Diphenhydramine): Uses & Side Effects
  11. 11
    Diphenhydramine: Uses, Interactions, Mechanism of Action
  12. 12
    Is Benadryl Still the Best Choice for Allergy Relief?

Related Topics:

#side effects #sleep aid #diphenhydramine #Benadryl #motion sickness #allergies #first-generation antihistamine #Syrup

Medical Disclaimer

This content is for informational purposes only and should not replace professional medical advice.