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If you miss a dose, take it as soon as you remember. If it is near the time of your next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

Take the tablet, capsule, or liquid form by mouth, with or without food. Diphenhydramine may be taken with food or milk if stomach upset occurs. If you are taking the suspension, shake the bottle well before each dose. Measure liquid forms of this medication with a dose-measuring spoon or device, not a regular teaspoon, to make sure you have the correct dose. The rapidly-dissolving tablet or strip should be allowed to dissolve on the tongue and then swallowed, with or without water. A second strip may be taken after the first strip has dissolved. The chewable tablets should be chewed thoroughly before being swallowed. Follow the directions for dosing on the label, or take as directed by your doctor. Do not take more medication than recommended. Your dosage is based on your age, medical condition and response to therapy. Ask your doctor or pharmacist if you have any questions. To prevent motion sickness, take your dose 30 minutes before starting activity such as travel. To help you sleep, take your dose about 30 minutes before bedtime. If you continue to have difficulty sleeping for longer than 2 weeks, contact your doctor. Tell your doctor if your condition does not improve or if it worsens.

Your healthcare professionals (e.g., doctor or pharmacist) may already be aware of any possible drug interactions and may be monitoring you for it. Do not start, stop or change the dosage of any medicine before checking with them first. Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: antihistamines applied to the skin (such as diphenhydramine cream, ointment, spray), antispasmodics (e.g., atropine, belladonna alkaloids), drugs for Parkinson's disease (e.g., anticholinergics such as benztropine, trihexyphenidyl), MAO inhibitors (e.g., furazolidone, isocarboxazid, linezolid, moclobemide, phenelzine, procarbazine, rasagiline, selegiline, tranylcypromine), scopolamine, tricyclic antidepressants (e.g., amitriptyline). Tell your doctor or pharmacist if you also take drugs that cause drowsiness such as: certain antihistamines (e.g., dimenhydrinate), anti-seizure drugs (e.g., carbamazepine), medicine for sleep or anxiety (e.g., alprazolam, diazepam, zolpidem), muscle relaxants, narcotic pain relievers (e.g., codeine), psychiatric medicines (e.g., chlorpromazine, risperidone, amitriptyline, trazodone). Check the labels on all your medicines (e.g., cough-and-cold products) because they may contain drowsiness-causing ingredients. Ask your pharmacist about the safe use of those products. This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

Do not take for several days before allergy testing because test results can be affected. Do not share this product with others.

If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US national poison hotline at 1-800-222-1222. Canadian residents should call their local poison control center directly. Symptoms of overdose may include large pupils, flushing, fever, hallucinations, weakness, shaking (tremor), muscle twitching, loss of consciousness, and seizures. In children, excitement may occur first, and may be followed by loss of coordination, drowsiness, loss of consciousness, and seizures.

Before taking diphenhydramine, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details. Before using this medication, tell your doctor or pharmacist your medical history, especially of: breathing problems (e.g., asthma, emphysema), glaucoma, heart problems, high blood pressure, liver disease, mental/mood changes, seizures, stomach problems (e.g., ulcers, obstruction), an overactive thyroid gland, difficulty urinating (e.g., due to an enlarged prostate gland). This drug may make you dizzy or drowsy or cause blurred vision. Do not drive, use machinery, or do any activity that requires alertness or clear vision until you are sure you can perform such activities safely. Limit the use of alcohol and certain other medications that cause drowsiness. (See also Drug Interactions.) To minimize dizziness and lightheadedness, get up slowly when rising from a seated or lying position. The rapidly-dissolving, liquid, and chewable preparations of this product may contain aspartame. If you have phenylketonuria (PKU) or any other condition that requires you to restrict your intake of aspartame (or phenylalanine), consult your doctor or pharmacist regarding the safe use of this medicine. Liquid preparations of this product may contain sugar and/or alcohol. Caution is advised if you have diabetes, alcohol dependence or liver disease. Ask your doctor or pharmacist about the safe use of this product. Caution is advised when using this drug in children because they are more sensitive to the effects of antihistamines. This drug can often cause excitement in young children instead of drowsiness. Caution is advised when using this drug in the elderly because they may be more sensitive to its effects, especially dizziness, drowsiness and low blood pressure. This drug should be used only if clearly needed during pregnancy. Tell your doctor if you are pregnant before using this medication. This drug passes into breast milk and may have undesirable effects on a nursing infant. Consult your doctor before breast-feeding.

Store at room temperature between 59-86 degrees F (between 15-30 degrees C) away from moisture and light. Store in a tightly closed container. Do not store in the bathroom. Do not freeze liquid forms of this medication. Keep all medicines away from children and pets. Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

Drowsiness, dizziness, headache, constipation, stomach upset, vision changes (e.g., blurred vision), irritability, decreased coordination, or dry mouth/nose/throat may occur. These effects may decrease as your body adjusts to the medication. If any of these effects persist or worsen, inform your doctor. To relieve dry mouth, suck on (sugarless) hard candy or ice chips, chew (sugarless) gum, drink water or use a saliva substitute. Diphenhydramine can dry up and thicken mucus in your lungs, making it more difficult to breathe and clear your lungs. To help prevent this effect, be sure to drink plenty of fluids unless otherwise directed by your physician. If your doctor has directed you to use this medication, remember that he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor immediately if any of these rare but serious side effects occur: pounding/irregular heartbeat, ringing in the ears, seizure, difficulty urinating. A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional. Diphenhydramine is also used alone or with other medications to treat shaking (tremor) and muscle stiffness caused by Parkinson's disease. It may also be used to treat side effects of certain psychiatric drugs such as involuntary movements and muscle stiffness (e.g., EPS). It works by blocking acetylcholine (See also Uses section).