Fentanyl is an opioid with multiple routes of administration, including intrathecal administration. The intrathecal use of fentanyl was started in the 1970s and is currently utilised in combination with general anaesthesia or as an adjuvant to local anaesthesia in prolonging the duration of analgesia and providing more effective post-operative analgesia. It exerts its action via mu receptors in the spinal cord and its analgesic effects by reducing the release of excitatory nociceptive neurotransmitters, gamma-aminobutyric acid, and glycine. Intrathecal fentanyl is used in various clinical settings, including perioperative pain management, day case surgery, obstetric practice (e.g., caesarean section), gynaecological surgeries, and major joint replacement surgeries. Specific side effects are associated with using intrathecal fentanyl. These include pruritus, respiratory depression, urinary retention, and hypotension. Amongst these side effects, pruritus is most commonly encountered. Intrathecal fentanyl has a comprehensive pharmacological and clinical profile, the understanding of which makes it a valuable opioid analgesic in anaesthesia and pain management.