Can I take Benadryl and NyQuil together?

What is in Benadryl and what is in NyQuil?

These are the active ingredients from each product's own Drug Facts label on DailyMed. Other versions of each brand can contain different ingredients, so check your exact box:

• Benadryl Allergy Liqui-Gels (per capsule): diphenhydramine 25 mg, an antihistamine. Adults and children 12 and over take 1 to 2 capsules every 4 to 6 hours, no more than 6 doses in 24 hours.
• NyQuil Cold & Flu liquid (per 30 mL): acetaminophen 650 mg (the drug in Tylenol), dextromethorphan 30 mg (cough suppressant), and doxylamine 12.5 mg, an antihistamine. Adults and children 12 and over take 30 mL every 6 hours, no more than 4 doses in 24 hours.
• The overlap: diphenhydramine and doxylamine are different drugs, but MedlinePlus puts both in the class called antihistamines. Both are the kind that make you sleepy.

Do the labels say not to combine them?

Not by name. The Benadryl label says do not use it with any other product that contains diphenhydramine, even one used on skin. NyQuil Cold & Flu does not contain diphenhydramine, so that line does not cover it. The NyQuil label's "do not use" warnings cover any other drug with acetaminophen and taking it with a prescription MAOI (a type of antidepressant) or within 2 weeks after stopping one. It does not mention other antihistamines.

That does not make the pair a good idea. Both labels say marked drowsiness may occur and that sedatives and tranquilizers may increase drowsiness, and both say to ask a doctor or pharmacist first if you take sedatives or tranquilizers. The NyQuil label adds the blood thinner warfarin to that list. The NHS lists "cough and cold remedies that also contain an antihistamine" among the medicines that could cause problems if taken with antihistamines. Taking both means 2 sedating antihistamines on top of each other.

What can happen if you take both?

The side effects of each one can add up. The NHS says drowsy antihistamines can cause sleepiness and reduced co-ordination, reaction speed and judgement, plus dry mouth, blurred vision and difficulty peeing. MedlinePlus lists dizziness and muscle weakness for diphenhydramine, and both MedlinePlus pages say to call a doctor right away for vision problems or difficulty urinating.

Both labels also say excitability may occur, especially in children. Both say to avoid alcohol, which adds to the drowsiness.

• Driving: the NHS says do not drive or use machinery after taking drowsy antihistamines. Do not drive until you are fully alert.
• Prostate, glaucoma or lung problems: both labels say ask a doctor before use if you have glaucoma, a breathing problem such as emphysema or chronic bronchitis, or trouble urinating due to an enlarged prostate. If any of these apply, ask before taking either one, and do not combine them.

Why should older adults be extra careful?

MedlinePlus says diphenhydramine generally should not be used in older adults, except to manage serious allergic reactions, because it is not as safe or effective as other medicines. It says older adults should not usually take doxylamine either, for the same reason. If you are 65 or older, it advises talking with your doctor about the risks and benefits.

The NHS also says older people should speak to a pharmacist or GP before taking an antihistamine. If you are buying cold medicine for an older parent, show the pharmacist their full medicine list. The combination of Benadryl and NyQuil gives them 2 of the drugs MedlinePlus says to usually avoid at once.

What should you do instead?

Choose one product for the night and match it to the symptom that bothers you most. NyQuil Cold & Flu already contains an antihistamine, and its label lists runny nose and sneezing among the symptoms it treats, so adding Benadryl gives you no new ingredient for those.

• Already took Benadryl tonight? Skip NyQuil. If you still need help with fever, aches or cough, ask a pharmacist about a product with a single active ingredient for that symptom, such as acetaminophen (Tylenol) for fever and aches.
• Already took NyQuil? Skip Benadryl. Also skip Tylenol and any other product with acetaminophen, because the NyQuil label says do not use it with any other drug containing acetaminophen.
• Watch for hidden diphenhydramine: MedlinePlus lists products that contain diphenhydramine in combination, including Advil PM, Motrin PM, Aleve PM, Excedrin PM, Theraflu Nighttime Severe Cold and Cough and Robitussin Night Time Cough and Cold. Do not pair any of these with NyQuil either. Advil PM and Motrin PM also contain ibuprofen, and Excedrin PM and Theraflu Nighttime Severe Cold and Cough also contain acetaminophen, which the NyQuil label says not to double up on.
• Kids: the Benadryl label says do not use it in children under 6, and NyQuil Cold & Flu says do not use under 4 and ask a doctor for ages 4 to under 12. The Benadryl label also says do not use it to make a child sleepy.

What if you already took both?

Do not take another dose of either one. Do not drive, do not drink alcohol, and do not take any other sleep aid or sedating medicine. It helps to have someone nearby who can check on you.

If you are not sure whether the amount you took is a problem, or you took more than the label dose of either product, call Poison Help at 1-800-222-1222. MedlinePlus gives this number for overdose of both diphenhydramine and doxylamine. Call 911 if someone collapses, has a seizure, has trouble breathing or cannot be woken up.