The group was visiting Khao Na Nai Luang Dharma Park in Surat Thani province on May 5 when they consumed ebony fruits growing in the area. Soon after, they began experiencing symptoms such as chest pain and vomiting, according to the Bangkok Post.
Emergency services were called to the scene, and five of the tourists agreed to be transported to a nearby hospital for treatment. The remaining two declined medical attention, Khaosod English reported.
Police said the group had traveled to the park in a chartered vehicle from Khao Lak in Phangnga province.
Authorities are investigating whether the symptoms were caused by toxins.