Wongtiraporn, W., Sangkarat, S., Laiwejpithaya, S., Pongriyawattana, S. and Chaudakshetrin, P. (1999) “A Comparison Study Between Oral Morphine Syrup and Morphine Intramuscular Injection in Premedication”, Siriraj Medical Journal, 51(2), pp. 86–91. available at: https://he02.tci-thaijo.org/index.php/sirirajmedj/article/view/246871 (accessed: 2 October 2026).