Shah was detained with about 13 grams (0.5 ounces) of marijuana at a hotel in Bangkok, according to an officer at Thonglor police station who did not want to be named.
"He borrowed a flash drive from hotel security and when the security guard entered his room to get his flash drive back he saw marijuana on the counter so he told police," the officer told AFP.
He said Shah, who is visiting Thailand on a tourist visa, had admitted illegal drug possession and was remanded in custody.
It is not the first time the former royal has been in trouble with the law in Thailand.
AFP