Benadryl Side Effects

Benadryl side effects and drug information

Diphenhydramine is an antihistamine, and Benadryl, which is its brand name, is an antihistamine medicine that works to lessen the reaction of the natural chemical histamine that is present in the body. Histamine can encourage signs of itching, runny nose, watery eyes, and sneezing.

Trade name Sominex, Unisom, Benadryl etc
Molar mass 255.355 g/mol
Formula C17H21NO
IUPAC ID N-dimethylethanamine
Soluble in Water


What is Benadryl

Benadryl functions to alleviate runny nose, effect of hives, skin rash, sneezing, itching and other symptoms of colds or allergy. Moreover, it also works as a treatment for motion sickness and some symptoms of Parkinson’s disease. This medicine can induce sleep, as well.

Side Effects of Benadryl

This medication causes some common side effects; that is why it would be best to know about them to provide safety precautions to the user.

Benadryl’s common side effects are:

  • For children, it may cause excitability
  • The user of this product may experience marked drowsiness, and cause hives so those who are driving or operating machinery should watch out for this reaction.
  • It is advised to avoid alcoholic drinks when using Benadryl as it may increase drowsiness.
  • Sedatives and tranquilizers must also be avoided when using this product as it can raise drowsiness as well.

Benadryl Indication and dosage

This medicine is meant to be used only for a short while, and only until the symptoms have cleared up. Advised to be taken as directed by the physician, or how the dosage says on the label. It should not be taken in either a smaller or larger amount than recommended, and never for a prolonged period.

Babies may also use this product, but upon doctor’s advice, and make sure to use the dosing syringe or the special dose-measuring spoon or medicine cup, whatever is provided. If the package does not come with a dose-measuring device, you may ask the pharmacist for one.

Benadryl is also useful for motion sickness, and for it to properly work, take it 30 minutes before doing the activity that will cause you motion sickness. Some of these situations may be a long car ride, boat travel, airplane, or amusement park rides.  

If you are doing an activity that will make you experience motion sickness for an extended duration, you may continue to take this medicine along with meals and at bedtime. For all the time that you know, you will be in this kind of situation.

If Benadryl is used as a sleep-inducing aid, take it within 30 minutes before going to bed.

Benadryl comes in liquid and capsule forms, where the tablet and liquid-filled capsule contains 25mg of diphenhydramine, and the liquid form for children contains 12.5mg per teaspoon.  

If using the capsule, do not open it. It should to be taken as a whole.

The liquid form of Benadryl, on the other hand, should be taken with a measuring dose device that comes with the product, and not use a kitchen spoon as it may not have the proper amount of dosage level.

General dosage

  • For children who are six years old and below, consult your pediatrician for proper dosage instructions.
  • For children between the ages of 6 and 11 years old, take one tablet or capsule every 4 to 6 hours, or if using the liquid form, take 1 to 2 teaspoons every 4 to 6 hours. Benadryl should only be used as needed.
  • For adults and children over 12 years old, take 1 to 2 capsule/s or tablet/s every 4 to 6 hours as needed.

Benadryl Drug Interaction

Diphenhydramine hydrochloride presents additive side effects if combined with CNS depressants such as hypnotics, sedatives, tranquilizers, and the like, and also alcohol. MAO inhibitors, on the other hand, increases and prolongs the drying effects of antihistamines.

Interaction with certain types of other drugs may cause some changes to how the medicine works or may have the potential to increase the risk for some serious side effects.  

When using this product, make sure to follow the proper dosage and do not try to start, stop, or even change the dosage unless directed by your physician. This rule also applies to any other medicines.  

Before using Benadryl, please make a list of all the other medicines that you are taking, and share the information with your doctor or the pharmacist whether they are prescription or nonprescription drugs and even herbal or supplement products.

Let them know if you are using any other medications or products that cause drowsiness like a cough or opioid pain relievers like hydrocodone and codeine, cannabis, alcohol, drugs for anxiety or sleep including zolpidem, alprazolam, and lorazepam; or muscle relaxants like cyclobenzaprine and carisoprodol, or other antihistamine drugs like chlorpheniramine and cetirizine. 

Antihistamine products applied to the skin, such as diphenhydramine spray, ointment, or cream, may cause some interaction to this medication.

Always check the labels of all medicines like cough, cold, or allergy products to know if it contains some ingredients that may trigger drowsiness. Do not hesitate to talk to the pharmacist or the doctor about the safe use of the product.

The use of this medication may also cause some reactions with some laboratory tests such as a skin allergy test and may interfere with the analysis and cause false results. Inform the lab staff and your doctor about your usage of this product.

Warnings and Precaution of Benadryl

Before starting medication with diphenhydramine or dimenhydrinate, let your doctor or pharmacist know if you are allergic to this ingredient, and if you have any other allergies. Benadryl may have some inactive components that can result in some allergic reactions or other complications.  

Be sure also to inform your doctor or pharmacist about your medical history. This is necessary, especially if you have the following medical conditions: difficulty in urination because of an enlarged prostate, stomach or intestine problems like blockage or ulcers, hyperthyroidism, seizures, liver disease, breathing problems like emphysema and asthma, heart problems, glaucoma or high blood pressure.  

The reaction of this drug on children usually causes them to be excited rather than feel drowsy, and they tend to be more sensitive to its side effects.

Some effects of taking Benadryl to older adults may include confusion, dizziness, trouble urinating, constipation, or drowsiness. The risk of drowsiness, confusion, and drowsiness is falling.

If pregnant, consult with your doctor first about the possible risks as well as the benefits when you take this medicine. But it should only be used when needed.

For breastfeeding mothers, it is essential to talk to your doctor first as this medicine passes into breastmilk and may cause some adverse reactions to the infant.

Clinical Pharmacology

Benadryl is available in the following different forms: liquid, tablets, and gel caps; and is a brand name for an antihistamine called diphenhydramine. This antihistamine is fully distributed in the entire body, which includes the CNS, and if any, there is only little that is excreted unchanged in the urine. Most appear as the degradation products of metabolic transformation in the liver, and most of which are entirely discharged in 24 hours. 

Diphenhydramine hydrochloride is known to be an antihistamine with anticholinergic and sedative reactions. One oral dose of diphenhydramine hydrochloride is easily absorbed by the body with a maximum activity happening in an average of an hour, with the next dose following from 4 to 6 hours. 

Antihistamines and histamines seem to compete for cell receptor sites on effector cells.  

Benadryl Medication Guide

For safety against having complications or experiencing more severe side effects, it is best first to consult your doctor if you are taking some other medications as this product may have drug interactions with the following:

  • Medications containing MAOI or monoamine oxidase inhibitor used to treat conditions such as depression, emotional or psychiatric, or for Parkinson’s disease.  
  • Products with diphenhydramine which includes the one applied on the skin.

This medicine cannot also be taken for two weeks after stopping a drug with MAOI. If you are unsure whether your prescription drug has an MAOI, it is advised to ask your doctor or pharmacist before starting with this medication.

Before using Benadryl, inform your doctor, especially if you have medical conditions such as:

  • Glaucoma
  • Thyroid disease
  • Heart disease
  • Diabetes
  • Persistent coughing as an effect of smoking, emphysema or asthma
  • High blood pressure
  • Problem urinating because of an enlarged prostate

Let your doctor or the pharmacist know if you are taking tranquillizers or sedatives as well.

This medicine should be used as prescribed, and nothing more or less as it may cause:

  • Marked drowsiness
  • Drowsiness may increase if used with alcohol, sedatives or tranquillizers
  • Excitability for children

When using this product, avoid alcoholic drinks and be careful in operating machinery or driving as it causes drowsiness.

Should any other symptoms appear, stop using the product and consult your doctor as these could be a sign of a serious condition:

  • Severe sore throat
  • Sleeplessness
  • Nervousness
  • Redness or swelling
  • Fever that lasts for more than three days or if it is getting worse
  • Pain, cough or nasal congestion that lasts for more than five days in children, and seven days for adults, or if any of these conditions are getting worse
  • A sore throat lasting for more than 2days and is either accompanied by or followed with: nausea or vomiting, rash, headache, swelling, or fever.
  • Recurring cough, or one that comes with rash or headache that does not go away

Pregnant women or breastfeeding mothers must consult their doctors first before using this product.

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