Benadryl is the brand name given to the drug diphenhydramine, most commonly used as an antihistamine for those suffering from allergy symptoms such as runny nose, itchy eyes and a sore throat. However, the drug is also used to help reduce dizziness, nausea and vomiting caused by motion sickness (e.g., carsickness, airsickness or seasickness). Benadryl is also used as a sleep aid. Diphenhydramine has also been used for treatment of tremors and muscle stiffness in those diagnosed with Parkinson's disease. However, as with many drugs and medications, side effects do occur, especially with long-term use.
Benadryl may have addictive effects on some people who engage in long term use of the drug, especially for those taking the medication as a sleep aid. Taking more Benadryl to achieve expected results is a common sign of the body's dependence on the drug. In some cases, insomnia may result.
Individuals who take Benadryl for extended periods of time may experience low blood pressure and heart palpitations, as well as occasional periods where it feels the heart is racing. Tightness of the chest, an abnormal heartbeat or restlessness may be an indication to see a physician.
Long-term use of Benadryl often affects mental cognition, especially in the elderly. Confusion, periods of inability to focus or concentrate, and anxiety are some symptoms experienced, as are agitation, moodiness and impatience. Depression and fatigue may also be evident. Some individuals have complained of hallucinations, nightmares and coordination problems.
Trembling, dizziness and vision complaints, including blurred or double vision are additional symptoms of the effects of long-term Benadryl use. Some people complain of a difficulty urinating as well as skin rash and headaches following long-term use.