What are medications i can buy that can suppress nightmares?

Keep dreaming: There is no such guaranteed selective nightmare supressor. Some meds will help by disrupting normal sleep architecture, causing less dreams in general. Dreams come in every shape and color, so the option is to not dream at all, or almost. Anyway, if nightmares are a symptom caused by certain diseases (ptsd, dissomnias, etc) the indicated med for it will probably diminish them. Sweet dreams.

By prescription : Prazosin is the medication that best suppresses nightmares. Both seroquel (quetiapine) and prazosin lower blood pressure. They may be used together as directed by your psychiatrist. Best wishes.