This is literally exactly the same as casting a curse. The three fold law is Wiccan dogma not a law of physics, so there is not bad karma for cursing. This is not even how karma works. Stop being holier then thou!
Essential oils from plants have been found to provide relief and healing for a wide variety of human conditions. As aromatherapy, they can treat depression, insomnia, and Attention Deficit and Hyperactivity Disorder (ADHD).