Which is stronger in morphine equivalence, oxycodone (OxyContin) 2.5mg or tramadol (Ultram) 25mg?

Oxycodone 2.5 mg is Stronger Than Tramadol 25 mg

Oxycodone 2.5 mg delivers approximately 3.75 mg morphine milligram equivalents (MME), while tramadol 25 mg provides only 5 mg MME, making oxycodone roughly 1.5 times stronger on a per-dose basis—but more importantly, oxycodone is a strong opioid with predictable analgesic effects while tramadol is a weak opioid with unreliable metabolism and significant limitations. 1

Morphine Equivalence Calculations

Direct MME Comparison:

• Oxycodone 2.5 mg = 3.75 MME (using the CDC conversion factor of 1.5) 1
• Tramadol 25 mg = 5 MME (using the CDC conversion factor of 0.2) 1

While tramadol appears slightly higher in raw MME, this calculation is misleading because:

Oxycodone's potency advantage:

• Oxycodone is consistently 1.5-2 times more potent than oral morphine across multiple guidelines 2, 1
• Oxycodone has 60-90% oral bioavailability, making it highly reliable 2
• Classified as a WHO Step III strong opioid with predictable analgesic effects 1

Tramadol's significant limitations:

• Tramadol is only 0.1-0.2 times as potent as morphine (approximately one-tenth) 2, 1
• Classified as a WHO Step II weak opioid with unreliable effects 1
• Functions as a prodrug requiring CYP2D6 metabolism, making efficacy highly variable between patients 1
• Maximum daily dose capped at 400 mg (80 MME) due to seizure risk 2, 1

Clinical Context That Matters

Why oxycodone is the stronger choice:

• The NCCN explicitly states tramadol is "less potent than other opioids and is considered to be approximately one tenth as potent as morphine" 2
• Oxycodone produces comparable analgesic effects to morphine with similar side effect profiles 2, 3
• Oxycodone has faster onset of analgesia than morphine, both IV and oral 4

Critical tramadol caveats:

• Tramadol should be used cautiously with serotonergic medications (TCAs, SSRIs, MAOIs) due to serotonin syndrome risk 2, 1
• Lower doses required in elderly patients (≥75 years) and those with hepatic/renal dysfunction to reduce seizure risk 2, 1
• A Cochrane review concluded tramadol is likely not as effective as morphine for cancer pain 2

Practical Algorithm for Clinical Decision-Making

Choose oxycodone 2.5 mg when:

• Reliable, predictable analgesia is needed 1
• Patient requires a strong opioid for moderate-to-severe pain 2
• Patient is on serotonergic medications (tramadol contraindicated) 2, 1

Tramadol 25 mg might be considered only when:

• Patient has mild-to-moderate pain not requiring strong opioids 2
• You need the dual mechanism (opioid + norepinephrine/serotonin reuptake inhibition) for neuropathic pain 2
• Patient is opioid-naïve and you want the weakest possible opioid trial 1

Common pitfall to avoid: Don't assume equal MME means equal clinical effect—tramadol's prodrug nature, ceiling dose, seizure risk, and classification as a weak opioid make it fundamentally less reliable than oxycodone despite similar MME calculations 2, 1.