Over-the-counter medications can be safe and effective for all kinds of mild ailments. 

However, just because a medication is over the counter, does not mean it can’t have severe side effects, or even be harmful if taken incorrectly. 

If you have fall or winter allergies and are searching for ways to get more sleep, you may be wondering how long Benadryl (diphenhydramine) lasts. We find answers to how long it lasts, how long it takes to kick in, how many pills you should take, how to combat drowsiness, and what side effects to look out for. 

How long does it take for Benadryl to kick in?

According to GoodRx, it generally takes about 15-20 minutes to start to feel the effects of Benedryl. If you are taking it for allergy symptoms, you may start to relief from itching, sneezing or coughing. You may also feel drowsy, which could be the desired effect if you are taking it as a sleep aid while congested. 

It’s important to note that using Benadryl as a sleep aid if you have no other symptoms may not be recommended. In an interview with Baylor College of Medicine, Dr. Philip Alapat, an assistant professor of medicine, says, “Using Benadryl or any antihistamine for sleep has no long-term benefit,” adding “most people develop a tolerance very quickly.”

How long does Benadryl last? 

When we take Benadryl, our body metabolizes or processes it. The concentration of the medication will reach its peak (highest point) around 2 hours after ingestion. Then, the concentration decreases in increments called half-lives. A half-life is the time it takes for the concentration of the medication to be cut in half. The length of the half-life is dependent on the person, but for this medication, it ranges from about 4 to 9 hours. For every half-life that passes, the amount of medication in your system will be cut in half. 

This is where it gets important – you may stop feeling the effects of the medication after about 4-6 hours, but Benadryl can be in your system for up to 60 hours. This is why it is vital to follow the instructions found on the package or given by your doctor, so you do not take too much. 

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How long will Benadryl make you sleepy?

You may feel drowsy for about 4-6 hours, but this can differ depending on the person. The best way to combat drowsiness caused by Benadryl (if this isn’t the goal) is to simply take a non-drowsy antihistamine like Zyrtec or Claritin. If drowsiness is the goal, you may want to take it about 30 minutes before bedtime. 

What are some of the side effects of Benadryl? 

According to the Cleveland Clinic, some of the common side effects of Benadryl include:

• Constipation
• Drowsiness
• Dry mouth
• Headache
• Upset stomach

RxList.com outlines some of the serious side effects:

• Pounding heartbeats or fluttering in your chest
• Painful or difficult urination
• Little or no urination
• Confusion
• Lightheadedness
• Tightness in your neck or jaw
• Uncontrollable movements of your tongue

If you are experiencing any of the above symptoms, you should seek medical attention as soon as possible. 

Can I take two Benadryl at once? 

An adult can take 1-2 tablets at a time, but no more than 6 tablets should be consumed in 24 hours. Be sure to follow any instructions on the package or ask your healthcare provider for further instructions. 

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