Benadryl is a brand name over-the-counter antihistamine medication. Histamine is a substance produced by the body in response to the presence of allergens like pollen, animal hair, or dust. Histamine release underlies certain symptoms like sneezing, itchy eyes, scratchy feelings in the nose or throat, runny nose, and difficulty breathing. Antihistamines like Benadryl combat the actions of histamine. Some people may also take Benadryl to reduce similar symptoms when they have a cold. Diphenhydramine is the main ingredient in this drug, and the substance can be found in other over-the-counter medications, too.1
Although Benadryl is sold without a prescription, the drug can cause drowsiness and sedation. Misuse of the medication may occur because people do not properly read the directions, mix it with alcohol or other intoxicants, or take too much of it at once. Any form of misuse can be dangerous and may result in severe side effects or an overdose.1
Just like with a prescription drug, it is important to follow the instructions on the package and only take Benadryl in recommended doses for a short period of time.
Even when taken as directed, Benadryl can have some troublesome side effects, so it is important to know how much is safe in one dose and in one day, and what the signs of abuse or overdose may be.
What Is Benadryl? How Is It Taken Safely?
Benadryl was the first antihistamine to receive approval from the Food and Drug Administration (FDA). The brand name was acquired by Johnson & Johnson in 2007 and the medication remains a widely-used treatment for allergies and mild cold symptoms.1
Since the medication has been available for several decades, safe dosage and elimination time are well understood. Benadryl is available in a variety of formulations, including tablets, liquid gels, and chewables. The standard dose of diphenhydramine in brand name Benadryl is 25 mg per dose for adults and 12.5 mg per dose in children’s formulas. For the average healthy adult, elimination half-life ranges from 6.7 to 11.7 hours.2 So between 6 to 12 hours after taking Benadryl, half the drug will be eliminated from the body. Within two days, the drug will be completely gone from the body.
Several factors impact how quickly Benadryl is metabolized, including: 3
- Age: Adults over 65 years old and children younger than 12 years old metabolize diphenhydramine more slowly, so lower doses less often are safer.3
- Liver problems: Since the active ingredient in Benadryl is processed through the liver, anyone with decreased hepatic function will have difficulty safely consuming this drug.
- Kidney problems: The kidneys help to process toxins by passing them out through the bladder. People who have decreased renal function may have a tough time metabolizing Benadryl. Urinary pH can also impact how the body processes diphenhydramine.
- Hydration: People who do not drink sufficient water may struggle to eliminate diphenhydramine from their system.
- Low vs. high dose: Even healthy adults who take more than the recommended dose of Benadryl will experience consequences, such as taking longer to metabolize the drug. Taking the recommended dose of Benadryl for longer than recommended may also lead to tolerance as the drug builds up in the body, and that also might increase the medication’s elimination time.
- Other medications: Taking prescription drugs, or other over the counter drugs, along with Benadryl may change how the body metabolizes all the substances together.
- Body weight/mass: Different body types process different amounts of medication at different rates. This is true for prescription drugs, recreational substances like alcohol, and over the counter drugs like Benadryl.
Although Benadryl is sold over the counter without a prescription, the active ingredient is potent and has an impact on the body. In addition to eliminating symptoms of allergies or a cold, it also interacts with other organ systems.
Even when taken as directed, Benadryl can cause side effects which include: 4
- Drowsiness or sleepiness.
- Dry mouth.
- Dryness in the nose or throat.
- Nausea or stomach upset.
- Jitteriness or restlessness.
- Tightness in the chest.
- Muscle weakness.
- Loss of appetite.
When the recommended amount is consumed, effects peak after about two hours. Within four hours, most effects of the medication wear off. There are still metabolites from diphenhydramine’s breakdown in the body, so taking another dose of Benadryl before the full effects wear off may be dangerous.5
Additionally, some people take more than the recommended amount because they want to get high. Benadryl produces mild sedative effects, and in larger amounts, that can feel like intoxication.
However, taking more than 25 mg can be extremely dangerous and is more likely to cause harm than produce any euphoria.5
Too much Benadryl can lead to an overdose and taking the drug with other potent substances can increase the risk of overdose.
For example, taking other antihistamines that contain diphenhydramine can lead to an overdose. Substances like alcohol or benzodiazepines (e.g., Valium, Xanax, Klonopin, etc.) may dangerously increase Benadryl’s sedative effects.
Muscle relaxants, sedative-hypnotic sleep medications like Ambien, tranquilizers, opioids, and other prescription drugs that are central nervous system (CNS) depressants can also adversely interact with Benadryl. In addition, some types of antidepressants called monoamine oxidase inhibitors (MAOIs) do not mix with antihistamines like Benadryl.3
Symptoms of a Benadryl overdose include: 6
- Enlarged pupils.
- Very dry eyes.
- Blurry vision.
- Ringing in the ears (tinnitus).
- Low blood pressure.
- Rapid heart rate.
- Agitation, rapid mood swings, or restlessness.
- Intense, sudden depression.
- Extreme drowsiness.
- Passing out or falling asleep.
- Nervousness or paranoia.
- Physical tremors.
- Unsteady gait, loss of balance, or inability to walk.
- Dry, red skin.
- Nausea or vomiting.
- Inability to urinate.
Attempting to Get High on Benadryl Can Be Extremely Dangerous
Benadryl is not effective as an intoxicant.Taking more than the recommended dose is more likely to lead to an overdose and uncomfortable side effects rather than euphoria. More than 500 mg, which is more than 40 times the recommended dose, may lead to a state of delirium, hallucinations, and other overdose symptoms. Anecdotal evidence about diphenhydramine highs indicates that the effects are more often uncomfortable and unsettling instead of enjoyable.
Attempts at getting high on Benadryl may be indicative of larger issues with addiction or substance abuse. Because Benadryl is easy to acquire, it may be the first drug abused by an adolescent, or it could be a drug abused after struggling with other substances. Regardless, it is important to get help ending substance abuse.
There are many risks in taking Benadryl long term, or mixing it with another drug or medication. If you have been abusing the prescribed dosage for Benadryl, it’s important to be informed about other potential signs that could lead to addiction.
- Benadryl (Diphenhydramine) – Side Effects, Dosage, Interactions – Drugs. https://www.everydayhealth.com/drugs/benadryl. Accessed June 24, 2019.
- Simons KJ, Watson WT, Martin TJ, Chen XY, Simons FE. Diphenhydramine: pharmacokinetics and pharmacodynamics in elderly adults, young adults, and children. J Clin Pharmacol. 1990;30(7):665-671. http://www.ncbi.nlm.nih.gov/pubmed/2391399. Accessed June 18, 2019.
- DIPHENHYDRAMINE – National Library of Medicine HSDB Database. https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb%3A%40term+%40DOCNO+3066. Accessed June 18, 2019.
- Diphenhydramine: MedlinePlus Drug Information. https://medlineplus.gov/druginfo/meds/a682539.html. Accessed June 18, 2019.
- How Long Does Benadryl Stay In Your System? – Mental Health Daily. https://mentalhealthdaily.com/2015/11/18/how-long-does-benadryl-stay-in-your-system/. Accessed June 24, 2019.
- Diphenhydramine overdose Information | Mount Sinai – New York. https://www.mountsinai.org/health-library/poison/diphenhydramine-overdose. Accessed June 18, 2019.