Scholars and journalists have shown that US state legislators often copy and paste policy text from other sources. This ‘policy plagiarism’ is perceived by critics as symptomatic of process failures and likely to undermine policy success. To proponents, copy and paste legislation stems from an efficient learning process likely to guarantee policy success. The authors test competing hypotheses by measuring success and plagiarism across three areas of US state policy: organ donation legislation, e-cigarette/vaping bans for minors and anti-bullying legislation. They find that higher levels of plagiarism result in significantly less success at reducing youth vaping rates and increasing organ donor registrations. They also find a negative, though not significant, relationship between copying and success for antibullying policy. The evidence favours opponents: legislators risk harming policy success by copying from others. This study of policy plagiarism advances knowledge by moving beyond the simple demonstration of the phenomenon to investigate the potential link between the copying of legislative text and the extent to which the policies studied achieved their goals.