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. 2026 Jul 30;18(7):e113648. doi: 10.7759/cureus.113648

Figure 2. Ionization, solubility, onset and duration of intrathecal opioids.

Figure 2

Hydrophilic opioids (i.e., morphine) have a slower onset and prolonged duration of action. Lipophilic opioids (i.e., fentanyl) demonstrate rapid onset and shorter analgesic duration.

Source: Ionization [27-29], Solubility [28,30], Onset and duration [31].