Valerian does not suppress the CNS. It acts more like a neuro hormone would, as opposed to a medication that changes chemicals of neuro-transmission. It enhances what the body is suppose to be doing, but due to stress is malfunctioning, if I may use simple terminology so laypersons understand, as well.

However, you are correct that it, or any other herb, can interact or interfer with precription medications, as well as, worsen a physical condition. So, no one should begin taking any herb without [1] doing thorough research on that herb and know its interactions and contraindications and [2] asking their doctor if he feels it is safe for them (unless totally healthy).

Herbs, after all, were medicine before pharmaceutical companies began making synthetic medications.