Words can contains heavy power inside them, but in the same way, lot of words are empty, and coming from not real, serious emotions, just from the ego, or from something else. If your emotions are true and enough intense, then yes, you can curse or even kill others (I did it before). Using words or not, whatever.
(You also can do some researches about cursed objects, and you’ll find out that lot of objects got cursed by a broken hearted, angry or deeply malevolent person. Their emotions was real, so you can imagine what you can do with your pure emotions. That’s why it’s important to learn how to control them, for these can be backfires to you.)