Diphenhydramine / pseudoephedrine Side Effects
For the Consumer
Applies to diphenhydramine / pseudoephedrine: liquid, sustained-release tablets, tablets
Other dosage forms:
Check with your doctor if any of these most COMMON side effects persist or become bothersome:
Seek medical attention right away if any of these SEVERE side effects occur while taking diphenhydramine / pseudoephedrine:
Constipation; diarrhea; dizziness; drowsiness; dry mouth, nose, and throat; excitability; headache; loss of appetite; nausea; nervousness or anxiety; trouble sleeping; upset stomach; vomiting; weakness.
Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); blurred vision or other vision changes; fast or irregular heartbeat; fever, chills, or persistent sore throat; hallucinations; mood or mental changes; persistent trouble sleeping; restlessness; seizures; severe dizziness, lightheadedness, or headache; severe drowsiness; tremor; trouble urinating or inability to urinate; unusual bruising or bleeding.
For Healthcare Professionals
Applies to diphenhydramine / pseudoephedrine: oral liquid, oral tablet, oral tablet disintegrating
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, and should avoid concomitant ingestion of alcohol.
Dystonic reactions to diphenhydramine have been accompanied by dizziness, mental confusion, rigidity, lip and tongue protrusion, trismus, torticollis, and swallowing difficulties. These reactions 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 small oral doses of diphenhydramine.[Ref]
Central nervous system (CNS) depression commonly occurs with diphenhydramine administration, resulting in drowsiness and sedation in nearly all patients treated. Motor skills may be impaired. Dystonic reactions have been reported after single doses of diphenhydramine.
Pseudoephedrine produces nervous system stimulation, resulting in tremor, anxiety, and nervousness. Insomnia is reported in up to 30% of pseudoephedrine-treated patients. Headache may also occur in patients receiving pseudoephedrine.[Ref]
Cardiovascular effects of diphenhydramine may include hypotension, tachycardia, and palpitations.
Cardiovascular adverse effects more commonly may be associated with pseudoephedrine. Pseudoephedrine generally causes a significant rise in heart rate. Hypertension and arrhythmias may be problematic in susceptible patients.[Ref]
Pseudoephedrine causes vasoconstriction which generally does not produce hypertension, but may be problematic for patients with pre-existing hypertension. Arrhythmias may be produced in predisposed patients. Rarely, pseudoephedrine has been reported to cause coronary artery spasm and chest pain.[Ref]
Hypersensitivity reactions may occur with diphenhydramine, generally resulting in rash, pruritus and eczema. Photosensitivity reactions have also been reported with diphenhydramine.
Hypersensitivity reactions to pseudoephedrine may also occur. Fixed drug eruptions secondary to pseudoephedrine have been reported.[Ref]
Most commonly, hypersensitivity to diphenhydramine manifests itself in patients receiving systemic drug after being sensitized to it by topical application. Sensitization with systemic administration has also been reported.[Ref]
Gastrointestinal tract adverse effects of diphenhydramine are mild, and may include nausea, dry mouth, and constipation.
Gastrointestinal adverse effects of pseudoephedrine may include anorexia and gastric irritation in approximately 5% of patients. Dry mouth, nose, or throat may occur in up to 15% of patients.[Ref]
Ocular affects of diphenhydramine may include blurred vision, diplopia, and dry eyes due to its anticholinergic effect.[Ref]
The genitourinary tract may be adversely affected due to the anticholinergic effects of diphenhydramine, resulting in urinary retention and dysuria.[Ref]
Hematologic adverse effects such as hemolytic anemia, thrombocytopenia, and agranulocytosis may be rarely caused by antihistamines.[Ref]
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2. Santora J, Rozek S, Samie MR "Diphenhydramine-induced dystonia ." Clin Pharm 8 (1989): 471
3. Stroh JE, Jr Ayars GH, Bernstein IL, Kemp JP, Podleski WK, Prenner BM, Schoenwetter WF, Salzmann JK "A comparative tolerance study of terfenadine-pseudoephedrine combination tablets and pseudoephedrine tablets in patients with allergic or vasomotor rhinitis." J Int Med Res 16 (1988): 420-7
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5. Brait KA, Zagerman AJ "Dyskinesias after antihistamine use ." N Engl J Med 296 (1977): 111
6. Lavenstein BL, Cantor FK "Acute dystonia: an unusual reaction to diphenhydramine." JAMA 236 (1976): 291
7. Loizou LA, Hamilton JG, Tsementzis SA "Intracranial haemorrhage in association with pseudoephedrine overdose." J Neurol Neurosurg Psychiatry 45 (1982): 471-2
8. Davenport PM, Wilhelm RE "An unusual vasculitis due to diphenhydramine. Cutaneous and central nervous system involvement." Arch Dermatol 92 (1965): 577-80
9. Roila F, Donati D, Basurto C, Del Favero A "Diphenhydramine and acute dystonia ." Ann Intern Med 111 (1989): 92-3
10. Tejera CA, Saravay SM, Goldman E, Gluck L "Diphenhydramine-induced delirium in elderly hospitalized patients with mild dementia." Psychosomatics 35 (1994): 399-402
11. Dickerson J, Perrier D, Mayersohn M, Bressler R "Dose tolerance and pharmacokinetic studies of L (+) pseudoephedrine capsules in man." Eur J Clin Pharmacol 14 (1978): 253-9
12. Jones B, Lal S "Tardive dyskinesia uncovered after ingestion of Sominex, an over-the- counter drug." Can J Psychiatry 30 (1985): 370-1
13. Filloux F "Toxic encephalopathy caused by topically applied diphenhydramine." J Pediatr 108 (1986): 1018-20
14. Gengo F, Gabos C, Miller JK "The pharmacodynamics of diphenhydramine-induced drowsiness and changes in mental performance." Clin Pharmacol Ther 45 (1989): 15-21
15. 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
16. Covington TR, Lawson LC, Young LL, eds. "Handbook of Nonprescription Drugs. 10th ed." Washington, DC: American Pharmaceutical Association (1993):
17. Gordon RD, Ballantine DM, Bachmann AW "Effects of repeated doses of pseudoephedrine on blood pressure and plasma catecholamines in normal subjects and in patients with phaeochromocytoma." Clin Exp Pharmacol Physiol 19 (1992): 287-90
18. Mariani PJ "Pseudoephedrine-induced hypertensive emergency: treatment with labetalol." Am J Emerg Med 4 (1986): 141-2
19. Wiener I, Tilkian AG, Palazzolo M "Coronary artery spasm and myocardial infarction in a patient with normal coronary arteries: temporal relationship to pseudoephedrine ingestion." Cathet Cardiovasc Diagn 20 (1990): 51-3
20. Rosen RA "Angina associated with pseudoephedrine ." Ann Emerg Med 10 (1981): 230-1
21. Camisa C "Fixed drug eruption due to pseudoephedrine." Cutis 41 (1988): 339-40
22. Coskey RJ "Contact dermatitis caused by diphenhydramine hydrochloride." J Am Acad Dermatol 8 (1983): 204-6
23. Emmett EA "Diphenhydramine photoallergy." Arch Dermatol 110 (1974): 249-52
24. Tomb RR, Lepoittevin JP, Espinassouze F, Heid E, Foussereau J "Systemic contact dermatitis from pseudoephedrine." Contact Dermatitis 24 (1991): 86-8
25. Shelley WB, Shelley ED "Nonpigmenting fixed drug eruption as a distinctive reaction pattern: examples caused by sensitivity to pseudoephedrine hydrochloride and tetrahydrozoline." J Am Acad Dermatol 17 (1987): 403-7
26. Lawrence CM, Byrne JP "Eczematous eruption from oral diphenhydramine." Contact Dermatitis 7 (1981): 276-7
27. Horio T "Allergic and photoallergic dermatitis from diphenhydramine." Arch Dermatol 112 (1976): 1124-6
28. Seedor JA, Lamberts D, Bergmann RB, Perry HD "Filamentary keratitis associated with diphenhydramine hydrochloride (Benadryl)." Am J Ophthalmol 101 (1986): 376-7
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Not all side effects for diphenhydramine / pseudoephedrine may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.
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