The over-the-counter medication diphenhydramine is found in many sleeping pills intended for insomnia treatment. It is the sleep-inducing element in medications such as Simply Sleep, Unisom, Tylenol PM, Advil PM, and Benadryl. Its use does not require a prescription, so it may be a good initial option for the treatment of acute insomnia to help initiate and maintain sleep. However, there is little evidence that diphenhydramine actually improves insomnia, and it may cause sleepiness the day after taking it. Doctors do not recommend routine use of diphenhydramine to treat insomnia.
Uses of Diphenhydramine
Diphenhydramine has many potential uses. As it does cause sleepiness, it is effective for the short-term treatment of insomnia or acute insomnia. It may help you get to sleep or stay asleep. In addition, it is often administered to relieve allergies or treat allergic reactions, and can be helpful in preventing motion sickness. It is also used to alleviate extrapyramidal symptoms, which may occur as a side effect of other medications.
How Does Diphenhydramine Work?
Diphenhydramine is part of a class of medications called antihistamines. It works at the level of neurotransmitters, which are the chemical messengers within the brain. It allows the neurotransmitter called histamine to build up in the spaces called synapses that are present between nerve cells. This leads to sedative effects and is accomplished by blocking its uptake into nearby cells. Diphenhydramine works both centrally within the brain as well as in peripheral nerve cells in other parts of the body. It possesses other effects and can suppress cough, nausea, and uncontrolled movements called dyskinesis.
Who Should Not Use Diphenhydramine?
Children less than 2 years old should not use diphenhydramine. Additionally, caution should be used when this medication is used by children younger than six years old and by the elderly. If you have increased intraocular pressure, such as in glaucoma, you should use diphenhydramine cautiously. Other conditions may also require caution, including individuals who have: hyperthyroidism, heart disease, high blood pressure, asthma, chronic obstructive pulmonary disease, pneumonia, peptic ulcer disease, prostate enlargement, bowel or bladder obstruction. If you have these conditions, you may wish to discuss your risk with your doctor before starting to use the medication.
Diphenhydramine has the potential to interact with some other drugs, especially those that affect the brain, so you may wish to review your medications with your doctor or pharmacist before using it.
What Are Common Side Effects of Diphenhydramine?
Some side effects that may commonly occur with diphenhydramine include:
- Diminished coordination or cognitive function
- Increased intraocular pressure
- Stomach discomfort
- Thick lung secretions
- Dry mouth or nose
- Difficulty urinating
- Low blood pressure
- Blurry or double vision
- Rapid or irregular heart rate
- Sensitivity to light
- Erectile dysfunction
What Are Potential Serious Reactions?
With the use of any drug, there are also risks of serious side effects. These occur more rarely. When using diphenhydramine, these may include:
- Anaphylaxis (severe allergic reaction including difficulty breathing)
- Low blood cell counts (agranulocytosis, anemia, thrombocytopenia, and leukopenia)
- Abnormal heart rhythms
- Toxic psychosis
- Acute labyrinthitis (inner ear problems)
Necessary Safety Precautions When Taking Diphenhydramine
As noted above, certain people should use diphenhydramine with caution, or not at all. It is an over-the-counter medication, so the risks are thought to be slightly lower compared to other prescription medications. Harm to a developing fetus is possible but unlikely, and diphenhydramine is probably safe in lactation, though caution is advised.
If you experience any difficulties, you should be in close contact with your primary health provider.
“Diphenhydramine.” Epocrates Rx Pro. Version 3.4, 2010. Epocrates, Inc. San Mateo, California.