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How Long Does Diphenhydramine Stay in Your System?

How Long Does Dephenhydramine Stay in Your System?

Diphenhydramine (Benadryl) is an antihistamine that’s often found in over-the-counter (OTC) allergy relief medications.

You can purchase OTC drugs at grocery stores, drug stores, and pharmacies without a prescription. Although diphenhydramine is commonly used in OTC medications, it can also produce a high and even cause dependence. The half-life of diphenhydramine determines how long its side effects last and how long it stays in a person’s body. Additionally, factors like weight, age, and the dosage taken can also influence the results of a drug test. So, how long does diphenhydramine stay in your system? Our Milford treatment center has your answers.

What Is Diphenhydramine Used For?

Sold under the names Benadryl, Sominex, Unisom, and others, diphenhydramine is most often used to treat symptoms of allergic reactions like sneezing, itchy eyes, scratchy feelings in the nose or throat, runny nose, and difficulty breathing. Diphenhydramine HCL is also sold as a sleep aid that helps people with insomnia or similar sleep disorders. Allergy symptoms occur when the immune system releases a substance called histamine in an attempt to protect the body from allergens like pollen, animal hair, or dust, and antihistamines like diphenhydramine work by combatting the symptoms of histamine. Benadryl is an antihistamine that, in addition to allergies, can also be used to treat cold symptoms, while its side effects include promoting sleep.

Although Benadryl is sold without a prescription, it can cause drowsiness, sedation, and a slight calm-like high. Diphenhydramine misuse can occur when a person takes more than the recommended dose or mixes it with another substance. While the first scenario is unintentional, the latter is a common form of recreational use. Drinks called “lean” and “purple drank” are substances that contain drugs like diphenhydramine as well as codeine, soda, hard candy, and alcohol. You can overdose on diphenhydramine, so it’s imperative to take it only as needed and as recommended. OTC drug use often opens the door to other forms of substance abuse, which facilitate the need for medical detox.

How Long Does Diphenhydramine Take to Work?

The body absorbs diphenhydramine within 20 and 30 minutes after the last dose. Diphenhydramine usually takes 15 minutes to work when taken orally. Side effects also peak anywhere between 2 to 4 hours after use. When injected, diphenhydramine side effects can kick in almost immediately. There is also topical administration of this drug to treat skin-related allergy symptoms. When applied topically, diphenhydramine can take around 24 hours to work.

Some common diphenhydramine HCL side effects include:

  • Dry mouth, nose, and throat
  • Drowsiness
  • Dizziness
  • Nausea or vomiting
  • Loss of appetite
  • Constipation
  • Increased chest congestion
  • Headache
  • Muscle weakness
  • Excitement or increased energy (especially in children)
  • Nervousness

More serious side effects of diphenhydramine include blurred vision, difficulty urinating or painful urination, and difficulty breathing. It is possible to overdose on diphenhydramine. If you experience any overdose symptoms like delirium, ringing in the ears, confusion, blurred vision, or hallucinations, get medical attention immediately.

How Long Does Diphenhydramine HCL Stay in Your System?

The diphenhydramine HCL half-life ranges from 2.4 hours to 9.3 hours but can average out to around 4.3 hours in young adults. A half-life of a drug determines how long it will take for 50% of it to flush out of your system. Depending on the median value that the individual lands on, diphenhydramine can stay in your system anywhere between 13.2 and 49 hours.

Factors that impact how long diphenhydramine stays in your system include:

  • Age: Adults over the age of 65 and children who are 12 and younger tend to metabolize diphenhydramine more slowly, meaning the drug can last longer in their systems.
  • Hydration: The more water you drink, the quicker diphenhydramine is flushed from the system.
  • Metabolism: Everyone’s body metabolizes or breaks down drugs and similar substances at a different rate. The faster your drug metabolism is, the less time diphenhydramine stays in your system.
  • Dose taken: Even healthy adults who take higher than the recommended dose of Benadryl will experience some unwanted side effects. Higher than recommended doses of diphenhydramine can take longer to metabolize and can lead to a build-up of tolerance in the body, increasing the medication’s elimination time in future uses.
  • Kidney health: The kidneys help to process toxins in the body and pass them out through the bladder. A person with kidney problems may have a tough time metabolizing diphenhydramine or Benadryl.
  • Liver health: Similar to kidney health, the health of your liver can also determine how long diphenhydramine stays in your system. Since the active ingredient in Benadryl is processed through the liver, anyone with liver problems may have difficulties safely using and metabolizing this drug.
  • Presence of other medications: As previously mentioned, taking other substances like prescription pills, alcohol, or other OTC drugs can change how the body metabolizes diphenhydramine. Mixing substances like this also increase the risk of overdose, so it’s important to be cautious when using any medications.
  • Bodyweight/mass: Different body types process drugs at different rates. Drugs tend to linger in fat, so individuals with higher levels of body fat may take longer to metabolize Benadryl and other similar drugs.

Although it usually takes around 500 mg of diphenhydramine to feel high or experience adverse side effects, any form of drug misuse can be dangerous. There are many risks in taking any drugs, whether OTC or prescription, for long periods of time. Diphenhydramine addiction is a real thing, and those who become dependent on it often require detox and inpatient drug treatment to recover. OTC drug use also tends to open the door to other forms of substance abuse, further increasing your likelihood of addiction and overdose.

If you or someone you know has a drug or alcohol problem, let Banyan Delaware help. Call us today at 888-280-4763 to learn more about our drug treatment programs in Milford.

Alyssa, Director of Digital Marketing
Alyssa, Director of Digital Marketing
Alyssa is the National Director of Digital Marketing and is responsible for a multitude of integrated campaigns and events in the behavioral health and addictions field. All articles have been written by Alyssa and medically reviewed by our Chief Medical Officer, Dr. Darrin Mangiacarne.