Two men were arrested in Phuket early on Wednesday after police found 100kg of kratom leaves on the back of their pickup truck.
The pickup was searched at a road checkpoint in Tambon Mai Khao in Phuket's Thalang district at 2am.
The two suspects were identified as Natee Madmanang, 49, from Songkhla and Thanan Chotechuan, 34, from Satun.
Natee said he was paid Bt15,000 by a man he knew only as Dam to deliver the kratom to a recipient in Tambon Koh Kaew in Phuket's Muang district. He said he paid Thnan Bt2,500 to accompany him.