Side Effects of Codeine and Guaifenesin Combination

Constipation is a universal side effect that should always be anticipated with prophylactic measures implemented in patients taking codeine, according to the American Society of Clinical Oncology 1, 2
Nausea and vomiting are frequent side effects, particularly during initial dosing of codeine, as reported by the American Society of Clinical Oncology 1, 2, 3
Sedation and dizziness may occur, especially in opioid-naive patients taking codeine, as noted by the American Society of Clinical Oncology 2
Variable efficacy and toxicity of codeine based on CYP2D6 metabolism can lead to poor metabolizers being essentially ineffective and ultrarapid metabolizers being potentially toxic due to excessive morphine production, according to the American Society of Clinical Oncology 1, 2
Anorexia and asthenia (weakness) are potential side effects of codeine, as reported by the American Society of Clinical Oncology 3
Vertigo is a possible side effect of codeine, as noted by the American Society of Clinical Oncology 3
There is a potential for dependence with prolonged use of codeine, which is a typical opioid concern, as reported by the American Society of Clinical Oncology 2

Clinical Considerations

Always implement constipation prophylaxis at treatment initiation with codeine, as recommended by the American Society of Clinical Oncology 1, 2
Monitor for excessive sedation, particularly in elderly patients taking codeine, as advised by the American Society of Clinical Oncology 1
Reassess the need for continued opioid therapy frequently in patients taking codeine, as recommended by the National Comprehensive Cancer Network 4
Total daily acetaminophen should not exceed 3-4g to prevent hepatotoxicity in patients taking other acetaminophen-containing products, as warned by the National Comprehensive Cancer Network 4

Codeine shows no clear superiority over other step 2 opioids (tramadol, dihydrocodeine) for cough suppression, and all have similar side effect profiles with nausea, vomiting, and constipation, as reported by the American Society of Clinical Oncology 1, 2, 3

The American Academy of Allergy, Asthma, and Immunology recognizes that combining a cough suppressant with guaifenesin is commonly used for symptomatic management of cough complicated by tenacious mucus, mucus plugs, or congestion—the same principle applies to codeine-guaifenesin combinations 5
Guaifenesin increases expectorated sputum volume, decreases sputum viscosity, and reduces difficulty in expectoration, while codeine provides cough suppression 5

Codeine has no or little analgesic or antitussive effect until metabolized to morphine via CYP2D6, making it essentially ineffective in poor metabolizers and potentially toxic in ultrarapid metabolizers 6, 7
Drugs that inhibit or compete for CYP2D6 may reduce the therapeutic effects of codeine 6
Constipation should always be anticipated in patients receiving codeine and prophylactic measures should be implemented 8
Codeine should be avoided in patients with liver cirrhosis since its metabolites may accumulate, causing side effects such as respiratory depression 9

Unlike anticholinergic medications, guaifenesin does not cause dry mouth, urinary retention, or cognitive impairment 10

Patients with productive cough due to upper respiratory tract infections who require both cough suppression and mucus clearance may benefit from this combination 5
Patients without contraindications to opioid use, such as liver cirrhosis, CYP2D6 ultrarapid metabolizer status, or concurrent CYP2D6 inhibitors, may be suitable for this combination 6, 7, 9
This combination should be avoided in patients with liver cirrhosis or significant hepatic impairment due to codeine accumulation risk 9
Known CYP2D6 poor metabolizers or ultrarapid metabolizers should avoid this combination due to efficacy and toxicity concerns 6, 7
Patients taking monoamine oxidase inhibitors or medications that significantly inhibit CYP2D6 should avoid this combination 6, 8