The two boxers are Seksan Or. Khwanmuang and Phet Authong Or. Khwanmuang.
They were believed to have been drugged after the morning weigh in, resulting in excessive urination. They were deemed unfit to fight that evening and were sent to hospital.
Seksan was scheduled for a main event against Superbank Mor. Rattanabandit, and Phet Authong was to meet Phet Tawee Sor. Kittichai.
The promoters withdrew both men from the card and promised to rescheduled the fights later.
Both boxers appeared in the ring to apologise to fans. After they stepped out of the ring and gave interviews, Phet Authong passed out and was rushed to hospital again.
Soonthorn Authong, a caretaker chief of Or. Khwanmuang camp, said the camp had strict security measures in place, particularly for beverages. The two boxers had trained in Chachoengsao before the fight and arrived back in Bangkok early Wednesday for the weigh in.
He bought energy drinks for both boxers in Chachoengsao and carefully packed them in a box with a lock. He said the camp will begin an intense investigation of the incident.