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Diphenhydramine
Diphenhydramine ( Benadryl®, Sominex ®, and many others) is an antihistamine medication available both over the counter and with a prescription. It comes in many different forms and is used for a variety of different purposes.
As with any medicine, diphenhydramine can cause side effects. However, not everyone who takes the drug will experience bothersome side effects. Some people tolerate it quite well. If side effects do occur, in most cases, they are minor and either require no treatment or can easily be treated by you or your healthcare provider. Serious side effects are less common. Of course, some "side effects" of diphenhydramine (such as drowsiness) are not considered to be side effects in certain situations (such as if you are taking the medication to sleep).
Common side effects of this drug include, but are not limited to:
- Drowsiness
- Dizziness
- Coordination problems
- Indigestion or heartburn.
(Click Diphenhydramine Side Effects to learn more, including potentially serious side effects that you should report immediately to your healthcare provider.)
What Should I Tell My Healthcare Provider Before Taking Diphenhydramine?
You should talk with your healthcare provider prior to taking this medication if you have:
Also, let your healthcare provider know if you are:
Make sure to tell your healthcare provider about any other medications you are taking, including prescription and non-prescription medicines, vitamins, and herbal supplements.
How Does Diphenhydramine Work?
Diphenhydramine is part of a class of drugs called antihistamines. Specifically, it is an H1 receptor antagonist. This means that it blocks a specific type of histamine receptor in the body (known as H1 receptors). Since allergic reactions are partly caused by the release of histamine from certain cells in the body, diphenhydramine can help relieve or prevent allergy symptoms.
Diphenhydramine also blocks acetylcholine receptors, an action which produces some of the bothersome side effects of the medication (such as dry mouth or difficulty urinating) but also makes the drug useful for some uses (such as for Parkinson's disease or for relieving a runny nose due to the common cold).
Like many antihistamines, diphenhydramine also works as a sedative. This action has made the medication useful as a sleep aid but also limits the usefulness of the medication for other uses (since drowsiness can be a bothersome side effect).
When and How to Take the Drug
General considerations include the following:
- This medication comes in many different forms. Depending on the particular product, it may be taken by mouth, applied to the skin, or injected into a vein or muscle.
- You can take diphenhydramine with food or on an empty stomach. If the medication seems to bother your stomach, try taking it with a little food.
- Because there are several different diphenhydramine products available, be sure to follow the instructions for your particular product.
- For the medication to work properly, it must be taken as directed.
Diphenhydramine Dosing Information
The recommended dose will vary, depending on a number of factors, including:
- The particular product
- The medical condition being treated
- Your age
- How you respond to diphenhydramine
- Other medications you are taking
- Other medical conditions you may have.
As is always the case, do not adjust your dose unless your healthcare provider specifically instructs you to do so.
What If I Take an Overdose of Diphenhydramine?
An overdose with this medication can cause serious problems. If you happen to take an overdose, seek immediate medical attention.
Diphenhydramine should be stored at room temperature, away from moisture and heat. Keep this and all other medications out of the reach of children.
What Should I Do If I Miss a Dose?
For people who take this medication on a regular schedule (such as for allergy treatment), if you do not take your dose as scheduled, take your missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose of diphenhydramine.
Diphenhydramine Strengths
There are many different strengths and forms available, including:
- Diphenhydramine 25 mg capsules, tablets, Liqui-Gels®, or quick-dissolving strips
- Diphenhydramine 50 mg capsules or tablets
- Diphenhydramine 12.5 mg per 5 mL liquid (12.5 mg per teaspoonful)
- Diphenhydramine 12.5 mg pre-filled single use spoons
- Diphenhydramine 1% and 2% cream
- Diphenhydramine 2% spray, gel, and stick
- Diphenhydramine 50 mg per mL injection (prescription only).
Diphenhydramine is also an active ingredient in many different combination products (such as cold or allergy products).
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Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD;
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