This single-centre, randomized, counterbalanced, within-subjects clinical trial compared four techniques for reducing pain and improving comfort during ventrogluteal intramuscular cyanocobalamin injection in adults. Participants presenting to a family health centre for prescribed vitamin B12 injection each received four injections, one with each technique: standard injection, internal rotation of the extremity, local cold application, and ShotBlocker. Technique order was assigned using a 4 x 4 Latin-square randomization. Pain and comfort were measured immediately after each injection using 0-10 participant-reported scales.

Adults aged 18 years or older who presented to TOKI Family Health Centre in Sivas, Turkey for prescribed cyanocobalamin intramuscular injection were enrolled between July and December 2019. Each participant received all four ventrogluteal injection techniques across four visits scheduled 24-48 hours apart. The order of techniques was randomized and counterbalanced using a 4 x 4 Latin-square sequence, with allocation concealed in sealed, opaque, sequentially numbered envelopes. Blinding of participants and the administering nurse was not feasible because the procedural techniques were visibly distinct, but the outcome assessor who entered and analyzed pain and comfort scores was blinded to sequence assignment until database lock. All injections were administered by the same experienced registered nurse using cyanocobalamin 1 mg in 1 mL and a 22-gauge, 38-mm needle. Pain was assessed using a 0-10 Visual Analogue Scale and comfort using a 0-10 numerical comfort scale immediately after each injection.

Inclusion Criteria:

• Adults aged 18 years or older.
• Presented to the family health centre for a prescribed course of cyanocobalamin intramuscular injection.
• Able to read, understand, and respond to study instruments in Turkish.
• Provided written informed consent.

Exclusion Criteria:

• Contraindication to ventrogluteal intramuscular injection.
• Local skin lesion, inflammation, edema, scarring, or sensory disturbance over either ventrogluteal site.
• Body mass index less than 18.5 or greater than 35 kg/m2.
• Concurrent regular analgesic or anti-inflammatory use.
• Chronic pain condition.
• Clinically diagnosed psychiatric disorder under active treatment.
• Pregnancy or lactation.
• Known cold intolerance, cold urticaria, or Raynaud phenomenon.

The datasets generated and analyzed during the study are not publicly available because the participant consent form did not include explicit permission for open data sharing. Data may be available from the corresponding author on reasonable request and subject to local ethics governance approval.

Participants and the administering nurse were not blinded because the procedures were visibly distinct. The outcome assessor who entered and analyzed pain and comfort scores was blinded to sequence assignment until the database was locked.