People with seasonal allergies, hay fever or the common cold may benefit from taking Benadryl, an over-the-counter antihistamine medication. Treatment with Benadryl, the brand name for the generic drug diphenhydramine, helps limit the action of an allergen-inducing substance, called histamine, in the body. Anyone who takes this medication should be aware of the side effects of Benadryl.
Dry Mouth
Patients taking Benadryl can develop dry mouth as a side effect of treatment. Dry mouth symptoms can include sore throat; increased thirst; oral pain or discomfort; or unusually sticky or thick saliva. These side effects are typically mild but may recur with subsequent dosing.
Sleepiness or Fatigue
Increased sleepiness or fatigue can occur in patients following treatment with Benadryl. Affected patients can become tired or may fall asleep shortly after taking a dose of this medication. This side effect can negatively impact a patient's level of alertness, and patients therefore should be careful when operating a motor vehicle or participating in potentially hazardous activities while taking Benadryl, warns RxList, an online drug index for consumers.
Headache
Benadryl can cause headache in certain patients, warns Drugs.com, a peer-reviewed drug information website. Headache symptoms can be uncomfortable and may interfere with a patient's ability to concentrate throughout the day. Severe or persistent headache side effects can be managed through the use of an over-the-counter pain medication, such as acetaminophen. These side effects are typically mild and progressively subside with continued Benadryl use.
Stomach Upset
Patients can develop an upset stomach as a side effect of taking Benadryl. These stomach upset effects can include nausea, vomiting, constipation or diarrhea, explains Pfizer, the pharmaceutical manufacturer of Benadryl. Constipation or diarrhea can contribute to additional side effects, such as abdominal bloating or cramping. Affected patients should contact a doctor if these side effects occur while taking Benadryl.
Mood-Related Changes
Additionally, Benadryl treatment can cause mood-related changes to occur in certain patients. These mood-related side effects can include agitation, irritability or confusion, warns the National Highway Traffic Safety Administration. Children who take Benadryl can appear unusually hyperactive or excited, which can make it difficult for them to fall asleep at bedtime. These side effects of Benadryl are typically temporary and subside once treatment ends. Patients who exhibit significant mood-related changes should seek additional care from a doctor.
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