Category 5: fine of up to Baht 1,500,000 (one million, five hundred thousand Thai baht) and imprisonment not exceeding 15 years;
If its for personal use like 1 gram that will just give you fine of maybe 2000baht and maybe maximum of 1 month prison time. It depends what you do with it, if you distribute it in large quantities then it applies to the high punishment. But if you have coka 1 gram it’s for sure prison time.
I am guessing category 5 is soft on persona use of the drugs and if you don’t have large amounts.
maybe I am totally wrong.