Trigger happy: Trigger‐responsive chain‐shattering polymerictherapeutics (CSPTs) were prepared by condensation polymerization of a UV‐ or hydrogen peroxide‐responsive domain and a drug as co‐monomers. Drug release can be started and stopped by starting and stopping the trigger treatment. Chemotherapeutic‐containing CSPTs showed trigger‐responsive in vitro and in vivo antitumor efficacy.