Im still confuzed about liniments ( sore no more)! help please!?

i have been told that sore no more liniment is toxic when injested and is a counter-irritant. is this true? is it ok to use before i ride to make my horse less stiff? does it cause any problems? it says its all natural and plant based so i assume its ok right? is arnica ok to be in a liniment? i want to use it mainly as a massage aid and to relax and help get rid of stiff muscles