Antonyms for the phrase "with no trouble" can be found among words like challenging, difficult, grueling, and arduous, among others. These words express the idea that an action or task requires considerable effort or skill to accomplish. They connote a sense of struggle, hardship, or adversity that needs to be overcome. Even more contrasting antonyms would include words like impossible, hopeless, or insurmountable, which suggest that something cannot be done without great difficulty or risk. These words often bring a sense of despair or discouragement, highlighting the magnitude of the challenge at hand.