This investigation examined the boundaries of inoculation theory by examining how inoculation can be applied to conspiracy theory propaganda as well as inoculation itself (called metainoculation). A 3‐phase experiment with 312 participants compared 3 main groups: no‐treatment control, inoculation, and metainoculation. Research questions explored how inoculation and metainoculation effects differ based on the argument structure of inoculation messages (fact‐ vs. logic‐based). The attack message was a 40‐minute chapter from the 9/11 Truth conspiracy theory film, Loose Change: Final Cut. The results indicated that both the inoculation treatments induced more resistance than the control message, with the fact‐based treatment being the most effective. The results also revealed that metainoculation treatments reduced the efficacy of the inoculation treatments.