Table 3.

Comparison among weak opioids for mild-to-moderate severity pain

Opioida	Main mode of action	Attributes	Precaution	Typical starting dose
Tramadol	μ-Opioid receptor agonist, 5HT- and NOR-reuptake blocker	Less constipation than other opioids	Nausea should be prevented by antiemetics; analgesia impaired in CYP2D6 poor metabolizers	25–50 mg q 4–6 h (IR); 50–100 mg q 12 h (CR)
Dihydrocodeine	μ-Opioid receptor agonist	Useful for patients with moderate pain, cough, and dyspnea	Constipation should be prevented by laxatives	30 mg q 4–6 h (IR); 60 mg q 12 h (CR)
Codeine	μ-Opioid receptor agonist	Useful for patients with moderate pain, cough, and dyspnea; combined formulations with paracetamol	Constipation should be prevented by laxatives; should not be administered in CYP2D6 ultrarapid metabolizers	30 mg q 4–6 h (IR); 60 mg q 12 h (CR)

^aTaken orally

5HT Serotonin; CR Controlled-release formulations; CYP2D6 Cytochrome P450 2D6; IR Immediate-release formulations; NOR Noradrenaline; q Every