ZzzQuil Side Effects
Generic Name: diphenhydramine
Note: This page contains side effects data for the generic drug diphenhydramine. It is possible that some of the dosage forms included below may not apply to the brand name ZzzQuil.
It is possible that some side effects of ZzzQuil may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.
For the Consumer
Applies to diphenhydramine: oral capsules and tablets, parenteral injection
Side effects include:
Sedation, sleepiness, dizziness, disturbed coordination, epigastric distress, thickening of bronchial secretions.
For Healthcare Professionals
Applies to diphenhydramine: compounding powder, injectable solution, oral capsule, oral disintegrating strip, oral liquid, oral tablet, oral tablet chewable, oral tablet disintegrating
Nervous system side effects have been reported frequently. These have included depression with drowsiness and sedation in nearly all patients treated. Motor skills may be impaired. Dystonic reactions have been reported after single doses of diphenhydramine (the active ingredient contained in ZzzQuil) [Ref]
The CNS depressant effect of diphenhydramine parallels its plasma concentrations. The plasma concentration threshold for sedation is 30 to 42 ng/mL, and to cause mental impairment is 58 to 74 ng/mL. Patients should be warned against driving while taking diphenhydramine.
Dystonic reactions have been accompanied by dizziness, mental confusion, rigidity, lip and tongue protrusion, trismus, torticollis, and swallowing difficulties and generally resolve spontaneously. Toxic encephalopathy has been reported in a child with chicken pox treated generously with topical diphenhydramine.
Delirium has been reported in elderly patients with mild dementia following a small oral dose of diphenhydramine.[Ref]
Hypersensitivity side effects have included rash, pruritus and eczema. Photosensitivity reactions have also been reported.[Ref]
Most commonly, hypersensitivity has manifested itself in patients receiving systemic drug after being sensitized to it by topical application. Sensitization with systemic administration has also been reported.[Ref]
Gastrointestinal side effects have been usually mild and included nausea and dry mouth.[Ref]
Cardiovascular side effects have included hypotension, tachycardia, and palpitations.[Ref]
Ocular side effects have included blurred vision, diplopia, and dry eyes due to anticholinergic effects.[Ref]
Genitourinary side effects have included urinary retention and dysuria as a result of the anticholinergic effects of diphenhydramine (the active ingredient contained in ZzzQuil) [Ref]
Hematologic side effects such as hemolytic anemia, thrombocytopenia, and agranulocytosis have been rarely caused by antihistamines.[Ref]
1. Etzel JV "Diphenhydramine-induced acute dystonia." Pharmacotherapy 14 (1994): 492-6
2. Brait KA, Zagerman AJ "Dyskinesias after antihistamine use ." N Engl J Med 296 (1977): 111
3. Davenport PM, Wilhelm RE "An unusual vasculitis due to diphenhydramine. Cutaneous and central nervous system involvement." Arch Dermatol 92 (1965): 577-80
4. Gengo F, Gabos C, Miller JK "The pharmacodynamics of diphenhydramine-induced drowsiness and changes in mental performance." Clin Pharmacol Ther 45 (1989): 15-21
5. Tejera CA, Saravay SM, Goldman E, Gluck L "Diphenhydramine-induced delirium in elderly hospitalized patients with mild dementia." Psychosomatics 35 (1994): 399-402
6. Borbely AA, Youmbi-Balderer G "Effect of diphenhydramine on subjective sleep parameters and on motor activity during bedtime." Int J Clin Pharmacol Ther Toxicol 26 (1988): 392-6
7. Carruthers SG, Shoeman DW, Hignite CE, Azarnoff DL "Correlation between plasma diphenhydramine level and sedative and antihistamine effects." Clin Pharmacol Ther 23 (1978): 375-82
8. Jones B, Lal S "Tardive dyskinesia uncovered after ingestion of Sominex, an over-the- counter drug." Can J Psychiatry 30 (1985): 370-1
9. Roila F, Donati D, Basurto C, Del Favero A "Diphenhydramine and acute dystonia ." Ann Intern Med 111 (1989): 92-3
10. Ramaekers JG, Ohanlon JF "Acrivastine, terfenadine and diphenhydramine effects on driving performance as a function of dose and time after dosing." Eur J Clin Pharmacol 47 (1994): 261-6
11. "Product Information. Benadryl (diphenhydramine)." Parke-Davis, Morris Plains, NJ.
12. Santora J, Rozek S, Samie MR "Diphenhydramine-induced dystonia ." Clin Pharm 8 (1989): 471
13. Lavenstein BL, Cantor FK "Acute dystonia: an unusual reaction to diphenhydramine." JAMA 236 (1976): 291
14. Sexton JD, Pronchik DJ "Diphenhydramine induced psychosis with therapeutic doses." Am J Emerg Med 15 (1997): 548-9
15. Vuurman EFPM, Vanveggel LMA, Sanders RL, Muntjewerff ND, Ohanlon JF "Effects of semprex-d and diphenhydramine on learning in young adults with seasonal allergic rhinitis." Ann Allergy Asthma Immunol 76 (1996): 247-52
16. Burns M, Moskowitz H "Effects of diphenhydramine and alcohol on skills performance." Eur J Clin Pharmacol 17 (1980): 259-66
17. Simons FER, Fraser TG, Reggin JD, Simons KJ "Comparison of the central nervous system effects produced by six h-1-receptor antagonists." Clin Exp Allergy 26 (1996): 1092-7
18. Richardson GS, Roehrs TA, Rosenthal L, Koshorek G, Roth T "Tolerance to daytime sedative effects of h1 antihistamines." J Clin Psychopharmacol 22 (2002): 511-5
19. Filloux F "Toxic encephalopathy caused by topically applied diphenhydramine." J Pediatr 108 (1986): 1018-20
20. Emmett EA "Diphenhydramine photoallergy." Arch Dermatol 110 (1974): 249-52
21. Horio T "Allergic and photoallergic dermatitis from diphenhydramine." Arch Dermatol 112 (1976): 1124-6
22. Coskey RJ "Contact dermatitis caused by diphenhydramine hydrochloride." J Am Acad Dermatol 8 (1983): 204-6
23. Barranco P, LopezSerrano MC, MorenoAncillo A "Anaphylactic reaction due to diphenhydramine." Allergy 53 (1998): 814
24. Lawrence CM, Byrne JP "Eczematous eruption from oral diphenhydramine." Contact Dermatitis 7 (1981): 276-7
25. Heine A "Diphenhydramine: a forgotten allergen?" Contact Dermatitis 35 (1996): 311-2
26. Yamada S, Tanaka M, Kawahara Y, Inada M, Ohata Y "Photoallergic contact dermatitis due to diphenhydramine hydrochloride." Contact Dermatitis 38 (1998): 282
27. Schuller DE, Turkewitz D "Adverse effects of antihistamines." Postgrad Med 79 (1986): 75-86
28. Seedor JA, Lamberts D, Bergmann RB, Perry HD "Filamentary keratitis associated with diphenhydramine hydrochloride (Benadryl)." Am J Ophthalmol 101 (1986): 376-7
29. Hopfenbeck JR, Cowley DS, Radant A, Greenblatt DJ, Roybyrne PP "Effects of diphenhydramine on human eye movements." Psychopharmacology (Berl) 118 (1995): 280-6
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