side effects of diphenhydramine

2 min read 09-03-2025

Diphenhydramine, commonly known by brand names like Benadryl, is an over-the-counter antihistamine frequently used to treat allergy symptoms like sneezing, runny nose, and itchy eyes. It's also a popular sleep aid due to its sedative effects. However, like all medications, diphenhydramine can cause side effects, ranging from mild to severe. This article explores the potential side effects, helping you make informed decisions about its use.

Common Side Effects of Diphenhydramine

Most people experience mild side effects when taking diphenhydramine. These are usually temporary and resolve once you stop taking the medication. Common side effects include:

Drowsiness: This is perhaps the most well-known side effect. Diphenhydramine's sedative properties can lead to significant drowsiness, impacting daily activities like driving or operating machinery. Avoid driving or engaging in activities requiring alertness if you feel drowsy.
Dry Mouth: Many users report experiencing dry mouth and throat. Drinking plenty of water can help alleviate this.
Constipation: Some individuals experience constipation. Increasing fluid and fiber intake may help.
Blurred Vision: Blurred vision is another common side effect. If this occurs, avoid tasks requiring sharp vision.
Dizziness: Lightheadedness or dizziness may occur, particularly when standing up quickly. Rise slowly to minimize this effect.
Nausea: Some people experience mild nausea.
Headache: Headaches can be a side effect, though they are often mild.

Less Common Side Effects

While less frequent, some users experience these side effects:

Difficulty Urinating: This is more common in men with an enlarged prostate.
Rapid Heartbeat (Tachycardia): In rare cases, diphenhydramine can increase heart rate.
Low Blood Pressure (Hypotension): Although uncommon, a drop in blood pressure is possible.
Excitement, Restlessness, or Irritability: This is particularly common in children. Paradoxically, in some individuals, instead of sedation, diphenhydramine can cause agitation.
Thickening of Respiratory Secretions: This is especially relevant for individuals with respiratory conditions.

Serious Side Effects: When to Seek Medical Attention

While rare, severe side effects can occur. Seek immediate medical attention if you experience any of the following:

Severe allergic reaction: Symptoms include hives, swelling of the face, lips, tongue, or throat, difficulty breathing, or a rapid heartbeat. This is a medical emergency.
Seizures: Diphenhydramine can rarely trigger seizures, particularly in individuals predisposed to them.
Hallucinations: Visual or auditory hallucinations are serious side effects that require immediate medical evaluation.
Liver damage: Although rare, liver damage is a potential serious side effect. Symptoms include jaundice (yellowing of the skin and eyes), dark urine, and abdominal pain.

Interactions with Other Medications

Diphenhydramine can interact with other medications. It's crucial to inform your doctor or pharmacist about all medications you are currently taking, including over-the-counter drugs, herbal remedies, and supplements. Interactions can increase the risk of side effects or reduce the effectiveness of other medications. This is especially critical for medications that cause drowsiness or affect the central nervous system.

How to Minimize Side Effects

Follow dosage instructions carefully: Never exceed the recommended dose.
Avoid alcohol: Alcohol can potentiate the sedative effects of diphenhydramine.
Avoid driving or operating machinery: Especially if you experience drowsiness.
Stay hydrated: Drink plenty of water to help with dry mouth and constipation.
Consult your doctor or pharmacist: If you have concerns or experience any unusual side effects.

Conclusion

Diphenhydramine is a useful medication for allergy relief and sleep aid. However, being aware of its potential side effects, both common and serious, is essential for safe usage. Always follow the dosage instructions, and consult a healthcare professional if you have any concerns or experience any adverse reactions. Remember, this information is for educational purposes and does not substitute for professional medical advice. Always consult a doctor or pharmacist before starting any new medication.