How Long Does Diphenhydramine (Benadryl) Stay in Your System?

Benadryl is an over-the-counter medication widely used to treat allergies, colds, and to help with sleep. Its active ingredient, diphenhydramine, works quickly to ease symptoms like sneezing, itching, and a runny nose.

This page explores what Benadryl is, how it works, and how long does Benadryl stay in your system. It also highlights the potential risks of misuse and what to watch for when combining it with other substances.

What Is Benadryl?

Benadryl is a popular OTC medication used to relieve allergy symptoms like sneezing, runny nose, itchy eyes, and skin rashes [1]. Many people also use it for cold symptoms, insect bites, and as a short-term sleep aid. Its ability to act quickly makes it a go-to remedy for occasional discomfort. 

The active ingredient in Benadryl—diphenhydramine—belongs to a group of medications called antihistamines [2]. These work by blocking histamine, a natural chemical in the body that triggers allergy symptoms. Benadryl is available in different forms, such as tablets, capsules, liquids, and creams.

Although it’s easy to buy, Benadryl is a powerful medication that must be used cautiously. Misusing it or taking more than the recommended dose can provoke severe health complications. 

Diphenhydramine

The main ingredient in Benadryl and other similar medications, diphenhydramine is a first-generation antihistamine, meaning it can cross the blood-brain barrier and cause drowsiness. This unique feature makes it helpful for people struggling with sleep problems or motion sickness.

Diphenhydramine works by blocking H1 receptors in the body [3]. These receptors are responsible for producing the effects of histamine. Histamine is what provokes allergy symptoms like swelling, itching, or sneezing when your body reacts to allergens like pollen or pet dander. 

While effective for allergies and other uses, diphenhydramine can also cause side effects like dry mouth, dizziness, and sedation. Take the medication only as directed and avoid combining it with CNS depressants like alcohol, which can worsen its effects. 

When To Take Benadryl

Benadryl can be taken for many reasons and should be used only when necessary and as directed. Common reasons include:

• Allergies: Use Benadryl to treat seasonal allergies or reactions to pet dander, dust, or mold. It can also help with hives or skin irritations caused by allergens.
• Cold symptoms: Benadryl may relieve a runny nose, sneezing, and watery eyes caused by colds.
• Insect bites: Its antihistamine properties help reduce swelling, itching, and redness from insect bites or stings.
• Sleep aids: Some people take Benadryl to help with occasional sleeplessness due to its sedating effects. That said, it should not be used as a long-term sleep solution.
• Motion sickness: Taking Benadryl before traveling can help reduce nausea or dizziness caused by motion. 

It’s best to take Benadryl about 30 minutes before you need it to start working. Always follow the dosage instructions on the label or given by a doctor. Avoid using it for more than a few days unless instructed by a healthcare provider.

Side Effects of Benadryl

Like any medication, Benadryl can cause side effects ranging from mild to severe.

Common side effects include:

• Drowsiness or feeling sleepy
• Dry mouth, throat, or nose
• Dizziness or lightheadedness
• Nausea or upset stomach
• Blurred vision
• Difficulty urinating 

These effects are more likely if you take a higher dose than recommended or if you are sensitive to antihistamines. 

Serious side effects include:

• Rapid or irregular heartbeat
• Severe confusion or agitation
• Difficulty breathing
• Hallucinations
• Seizures

 If you experience any of these severe side effects, you should stop taking Benadryl and seek medical attention immediately.

Using Benadryl regularly over a long period can lead to the development of tolerance, meaning the medication may not work as well [4]. It can also increase the risk of memory problems or other cognitive issues, especially in older adults.

Consult your doctor if you have underlying conditions like asthma, glaucoma, or liver disease before using Benadryl. 

How Long Does Diphenhydramine Last?

How long does Benadryl last is anywhere from 4 to 6 hours. After this period, the symptoms it was treating may gradually return as the medication wears off. this timeline can vary depending on age, weight, metabolism, and dosage. 

The sedative effects of diphenhydramine begin within 30 minutes, making it effective for allergies and sleep-related issues. However, these effects might linger longer in some people, especially those who metabolize drugs more slowly. Older adults and children, for example, might feel its effects for longer due to differences in how their bodies process the medication.

For most people, the noticeable effects of the medication are gone within 6 hours. That said, it may remain detectable in the body for longer with repeated doses.

How Long Do Antihistamines Stay in Your System?

Antihistamines, including diphenhydramine, vary in how long they stay in your system based on the type of antihistamine and individual factors.

1. First-generation antihistamines like diphenhydramine: These are known for their sedating effects. They usually stay in the system for 24 to 48 hours, but their primary effects wear off within 4 to 6 hours.
2. Second-generation antihistamines like loratadine and cetirizine: These are non-sedating and last longer in the body, often providing relief for 24 hours with a single dose. Factors that influence how long antihistamines remain in the system include:

• Metabolism: Faster metabolisms clear medications more quickly.
  Age: Older adults process drugs differently, which may lengthen or shorten the time antihistamines stay in the system.
• Liver and kidney health: These organs help break down and eliminate medications. Health issues here can slow the process.
• Dosage and frequency: Higher doses or repeated use can lead to accumulation in the body.
• For most people, antihistamines like Benadryl will be almost eliminated within a day or two. 

How Long Does It Take for Benadryl to Wear Off?

Benadryl’s effects usually wear off within 6 hours after a single dose. While it may relieve symptoms quickly, its drowsy side effects can linger. Do not drive or operate machinery during this time.

The medication’s active ingredient, diphenhydramine, has a half-life of 3 to 9 hours, meaning it takes this long for the body to clear half the dose from your system. After about 24 hours, most of the drug is usually gone. 

Some people might notice side effects like dry mouth or grogginess after the main effects have worn off. This is more common in children, seniors, or individuals with slower metabolisms.

How Long Does It Take for 25mg of Benadryl to Wear Off?

A standard dose of Benadryl—25mg for adults—begins working within 30 minutes and provides relief for 4 to 6 hours. After that, its effects gradually decrease as the body metabolizes the medication. 

For most people, the drug is significantly reduced in the bloodstream within 12 to 24 hours. However, those with slower metabolisms or health issues affecting the liver or kidneys may experience prolonged effects.

To speed up the process of wearing off, stay hydrated and avoid taking additional doses. This helps your body metabolize and eliminate the medication more efficiently. 

What Is Benadryl Half-Life?

The half-life of Benadryl refers to how long it takes for half of the drug to be eliminated from the body. On average, the half-life of diphenhydramine ranges from 3 to 9 hours [5]. This means that within this timeframe, half of the medication has been metabolized and removed.

For most people, it takes about 5 half-life cycles to eliminate the drug from the system. This process can vary depending on age, metabolism, and health. For example, older adults and people with liver or kidney conditions may metabolize the drug more slowly, causing it to remain in the body for longer. 

While Benadryl’s half-life provides an estimate of how long it stays in the body, its sedative effects usually wear off much sooner—typically within 4 to 6 hours. Understanding its half-life is helpful if you’re trying to avoid side effects or plan for activities like driving or working. 

How to Make Benadryl Wear Off Faster

If you’ve taken Benadryl and want its effects to wear off more quickly, there are some steps you can take. That said, avoid risky methods like taking other substances to counteract its effects, which can lead to harmful interactions.

• Stay hydrated: Drinking plenty of water helps your body flush out the medication through your kidneys. Staying hydrated can support faster elimination of Benadryl.
• Engage in light exercise: Gentle physical activity can increase your circulation and metabolism, helping your body process the drug more efficiently. Avoid intense exercise, as the sedative effects may affect coordination or balance.
• Eat a nutritious meal: Consuming healthy foods can support your body’s metabolism, giving it the energy needed to process the medication.
• Get fresh air: Going outside for a walk or spending time in fresh air may help you feel more alert as the sedative effects of the medication wear off.
• Avoid alcohol or other drugs: These substances can intensify drowsiness or interact with Benadryl, potentially making the situation worse. 

The best approach is to give your body time to metabolize the drug naturally. If you are experiencing prolonged or severe side effects, consult a doctor.

5 Factors That Affect How Long Benadryl Lasts

The length of time Benadryl lasts in your system can vary widely between individuals. Here are five key factors that influence its duration:

1. Dosage: Larger doses take longer to metabolize and leave your system. For instance, a 50mg dose may take more time to wear off than a standard 25mg dose.
2. Age: Older adults and children process medications differently. Older individuals may experience prolonged effects, while children might metabolize Benadryl more quickly or experience unusual side effects, such as excitement instead of drowsiness.
3. Body weight and fat: People with higher body fat percentages may store diphenhydramine longer, as the drug can bind to fat tissues. Conversely, those with lower body fat may metabolize it faster.
4. Metabolism: Individuals with faster metabolisms tend to clear drugs from their systems more quickly. Factors like regular exercise, diet, and genetics all play a role in metabolism speed.
5. Liver and kidney function: These organs are responsible for breaking down and eliminating medications. If you have liver or kidney conditions, the drug may stay in your system for a longer period.

Dangers of Benadryl Misuse

While Benadryl is widely available and generally safe when used correctly, it can be dangerous if misused. Misuse occurs when people take larger doses than recommended, use it more frequently than advised, or combine it with other substances like alcohol or recreational drugs. Common reasons for misuse include:

• Seeking a high: In high doses, diphenhydramine can cause hallucinations or a calming effect, leading some to abuse it recreationally.
• Sleep aid dependence: Some people use Benadryl regularly to help them sleep, which can lead to tolerance and overuse.
• Unintended overdose: Accidentally taking too much Benadryl, especially when combined with other medications containing diphenhydramine, is a common form of misuse. 

The health risks of misuse are: 

• Severe drowsiness or confusion
• Increased risk of accidents or falls
• Heart problems, including arrhythmias
• Cognitive issues or memory problems over time
• Increased likelihood of addiction to sedative effects

Benadryl misuse can lead to long-term health consequences. If you or someone you know is misusing this medication, seek professional help to address the issue safely. 

Overdose Symptom of Benadryl

Taking too much Benadryl can result in an overdose, which can be life-threatening if not treated promptly. Overdoses may occur accidentally or due to intentional misuse. Symptoms include: 

• Extreme drowsiness or confusion
• Rapid heartbeat (tachycardia)
• Seizures
• Hallucinations
• Difficulty breathing
• Inability to urinate
• Dilated pupils or blurred vision

In severe cases, a Benadryl overdose can cause coma or death. If you suspect an overdose, call 911 or seek emergency medical attention immediately. Acting quickly can save a life. 

Interactions With Other Substances

Benadryl can interact with many substances, including medications, alcohol, and recreational drugs. Leading to serious side effects or health risks. Common interactions to watch for include:

• Alcohol: Combining Benadryl with alcohol can intensify drowsiness, impair coordination, and increase the risk of accidents.
• Sedatives and tranquilizers: Drugs like benzodiazepines or opioids can dangerously amplify the sedative effects of Benadryl, increasing the risk of respiratory depression.
• Other antihistamines: Taking multiple antihistamines, whether OTC or prescription, can lead to an overdose of diphenhydramine.
• OTC medications: Many cold and flu products also contain diphenhydramine. Accidentally doubling up can result in dangerous levels of the drug.
• Antidepressants: Some antidepressants, especially those with anticholinergic effects, can interact with Benadryl and cause dizziness, confusion, or heart problems. 

To avoid harmful interactions, always read medication labels and consult your doctor before taking Benadryl with other substances. 

Achieve Lasting Recovery with Renaissance Recovery’s Compassionate, Insurance-Covered Treatment

If you have been misusing Benadryl, we can help you address dependence and learn coping skills at Renaissance Recovery. 

When you choose an outpatient program at one of our California or Florida rehabs, you can carry on at work or school and live at home while getting first-class addiction treatment during weekday sessions. All treatment plans are personalized, with therapies like:

• Medication management
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• Family therapy
• Group therapy
• Holistic treatments
• Aftercare

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Sources 

[1] https://www.drugs.com/benadryl.html 

[2] https://medlineplus.gov/druginfo/meds/a682539.html 

[3] https://www.ncbi.nlm.nih.gov/books/NBK526010/ 

[4] https://pubmed.ncbi.nlm.nih.gov/11224198/ 

[5] https://www.ncbi.nlm.nih.gov/books/NBK526010