Understanding How Long Does Benadryl Last? Effects, Duration & What to Expect

Benadryl (diphenhydramine) is a common go-to medication used for allergies, colds, sleeping troubles, and motion sickness. If you are taking it to relieve itchiness or cold and want to avoid its unwanted side effects, you might be wondering, How long does Benadryl last? Understanding the duration of its effect is crucial for safe use. This blog will guide you on how long the effect of Benadryl lasts and what factors affect it. Additionally, we’ll discuss its side effects and safe usage tips to avoid those effects! Read on!

How Long Does Benadryl Last?

The effects of Benadryl (diphenhydramine) typically last for 4-6 hours. It starts showing its effects within 15-30 minutes after its intake and reaches its peak effect within 2-3 hours. If you take the extended-release version of Benadryl, its effectiveness will last for around 12 hours. After this time period, its effects subside, however, its metabolites can remain in the system for a longer time. 

How Long Does Benadryl Stay in Your System?

The Benadryl half-life is around 3.4-9.2 hours. Basically, the half-life is the time that active metabolites of the drug take to reduce by half. This means that it takes approximately 24-48 hours for the body to completely eliminate the drug. However, this duration can vary in different drug tests due to the test's sensitivity level, the testing method used, the drug being tested for, individual metabolism, and the drug dose taken.

Detection Window of Benadryl Based on Drug Tests

These detection periods are based on the amount of time of its last use. The exact value can vary depending on a variety of factors.

Important for drug tests: If you’re undergoing a test for legal or employment reasons, inform the examiner about any antihistamines you’ve taken to avoid false positives.

Factors That Affect How Long Benadryl (Diphenhydramine) Lasts

These factors can increase or decrease the effect of Benadryl (diphenhydramine):

• Dosage: The higher the doses, the longer the Benadryl may take to get metabolized and eliminated.

• Metabolism: Individuals with a faster metabolism may more quickly clear the drug metabolites than ones with a slower metabolism.

• Frequency of Use: Frequent or repeated use may lead to a huge buildup of the drug in the system, thus, extending its stay.

• Age: Older adults might experience prolonged effects as they take longer (around 18 hours) to metabolize and excrete the drug.

• Body Fat: Individuals with higher body fat might store the drug for a longer period, extending its elimination.

• Kidney & Liver Health: Impaired liver & kidney function can respectively slow down drug metabolization and elimination

How Long Does Benadryl (Diphenhydramine) Make You Drowsy?

Benadryl (Diphenhydramine) will make you feel drowsy or sleepy for about 4 to 6 hours. However, this time frame can vary depending on the individual. The sedation or drowsy effect of Benadryl can last for 8 hours and may also continue for the next day if consumed at night. But, avoid its long-term use as research reports a high risk for dementia.

The best way to fight off drowsiness and sleepiness is to use non-drowsy antihistamines such as Claritin or Zyrtec. If you want to feel sleepy, you can take it about 30 minutes before going to bed. 

Side Effects of Benadryl

While taking Benadryl, keep a watch over the potential side effects to prevent further complications due to their lasting effects.

Common side effects:

• Constipation

• Drowsiness

• Upset stomach

• Dry mouth

• Headache

Serious side effects:

• Pounding heartbeats

• Lightheadedness

• Confusion

• A fluttering feeling in the chest

• Painful or trouble urination

• Less or no urination

• Tightness in the neck or jaw

• Uncontrollable movements of the tongue

If you experience any symptoms, immediately seek professional help.

How To Quickly Get Rid of Benadryl Effects?

If you are taking Benadryl and want to prevent its side effects, follow these tips:

• Stay Hydrated: Drink a lot of water to quickly flush out the drug from the system via urine.

• Practice Light Exercise: Engage in walking or physical activities to boost your metabolism, helping the body with effective drug processing.

• Consume Nutritious Foods: Add lean protein, whole grains, vegetables, and dairy products to your diet to support the body's detox process.

• Avoid Alcohol & Other Drugs: Avoid them to prevent prolonged drowsiness or increase the risk of side effects.

• Get Fresh Air: Getting fresh air can make you more alert when Benadryl's sedative effects wear off.

• Be Patient: Maintain patience as Benadryl’s effects naturally subside within 4 to 6 hours.

Note: If symptoms worsen or persist, see a doctor as soon as possible!

Tips to Safely Take Benadryl

To prevent the risk of Benadryl's side effects, consider these steps for its safe use:

• Take as directed: Make sure to use the medicine as prescribed by the doctor. Overdose can lead to complications.

• Have with or without food: Take it with or without food, but, in case of an upset stomach, have it with milk or food to prevent an upset stomach.

• Avoid driving: As the medicine impacts your judgment and makes you drowsy, avoid driving or heavy machinery until you feel completely better.

• Use with caution in children: Don't give it to children below 12 years at night as a sleep aid because it can make them more nervous, agitated, or alert, troubling their sleep.

• Avoid combining it with alcohol: Don't mix it with alcohol to prevent an increased risk of drowsiness and other potential side effects.

• Be specific during motion sickness: Make sure to use it for 30 minutes before traveling anywhere.

• Consult a gynecologist during pregnancy and breastfeeding: Always consult the doctor before using Benadryl during these phases as there are no appropriate well-controlled studies for its safe use.

• Check for drug interactions: Discuss your other current medications with your doctor to avoid harmful interactions. Those medications may include:

1. Benzodiazepines like Xanax and Valium
2. Other antihistamines such as loratadine and hydroxyzine
3. Antipsychotic drugs
4. Opioids
5. Antidepressants
6. Anticholinergic drugs

Understanding Benadryl Overdose Symptoms

Accidental or intentional, excessive use of Benadryl can cause overdose risk which can be fatal if left untreated. You be aware of these overdose symptoms: 

• Extreme drowsiness

• Confusion

• Hallucinations

• Rapid heartbeat

• Seizures

• Difficulty breathing

• Inability to urinate

• Dilated pupils

• Blurred vision

Important Note: Overdosing can lead to coma and even death in severe cases. Hence, if you notice any of these symptoms, call 911 for emergency medical attention or 800-222-1222 for poison center services. 

Benadryl Withdrawal Symptoms

It's not recommended to take Benadryl for more than 2 weeks as it can lead to dependency and even stop showing its effects to reduce allergy symptoms. So, if you are dependent on this medication and experiencing its side effects, don't discontinue it without a doctor's guidance. Sudden stopping can lead to severe withdrawal symptoms that you should be aware of to avoid such a situation.

The following are the potential withdrawal symptoms of Benadryl that you need to report to your doctor immediately:

• Nausea

• Vomiting

• Extreme headaches

• Hallucinations

• Severe body pain

• Sweating and tremors

• Fever and palpitations

• Rebound Sleeplessness

• Seizures

• Anxiety attacks

Safer Alternatives to Benadryl

You can take these safer alternatives to Benadryl as they bring fewer side effects like drowsiness and have great safety records:

• Cetirizine (Zyrtec)

• Loratadine (Claritin or Alavert)

• Fexofenadine (Allegra)

• Levocetirizine ( Xyzal)

• Desloratadine (Clarinex)

Final Thoughts

So, how long does Benadryl last? Well, as we learn in this article, it typically lasts for 4-6 hours, with its effect kicking it within 15-30 minutes of its last use and reaching its peak effect in about 1-2 hours. However, though its effects wear off after 6 hours, its metabolites still linger in the system which can be detectable through different drug tests. So, if you have concerns regarding Benadryl's side effects, consult your doctor. In case you are soon undergoing a drug test, discontinue its use under medical supervision.

But, if you are struggling with addiction, consider an effective treatment plan.

Read Also: How Long Does Valium Last?