Some of these may be due to overdose, others to individual intolerance to the medication. Most antihistamines cause some people to become drowsy. Make sure you know how you react to the drug you are taking before you drive or operate machinery. The elderly may be particularly susceptible to the sedative effect. Do not give antihistamines to children under 6 years without consulting a doctor.
Antihistamines add to the effects of alcohol and other depressants.
Therefore, avoid taking them close to the same time you drink alcohol or use drugs that slow down the nervous system, such as sedatives, tranquilizers, sleeping pills, narcotics, prescription pain medicines, seizure medications, muscle relaxants, or anesthetics. Antihistamines may also mask nausea associated with overdose from other medicines you are taking or from other medical conditions. If you suspect such effects while taking antihistamines, be sure to inform your doctor. If you get skin tests for allergies or are receiving allergy injections, tell your doctor if you are taking antihistamines because these drugs can distort test results and mask reactions. For relief of dry mouth, nose and throat caused by antihistamines, use sugarless candy or gum or melt pieces of ice in your mouth.