Spices have strong flavoring power so its better to use less than more, so I would recommend (1-1.6)% . you can reduce the concentration depending on  what  customers may want but you cant go beyond 2% because the ingredient is psychoactive at higher doses  and  can make the product inedible and its toxicity can last for over 24 hrs .And maybe the challenging part of it would be with the efficacy of the ingredient and difference of the threshold of  toxicity to different people