Cancer is an important issue and a model topic for misinformatfion researchers. The present research experimentally investigates the effect of cancer-related conspiracy beliefs and misinformation on oncology treatment intentions in a cancer-free population. In three pre-registered studies (N total = 1020), participants were asked to put themselves in the shoes of a patient recommended for chemotherapy. Study 1 (N = 300) failed to experimentally manipulate cancer-related conspiracy beliefs with exposure to a health scandal not related to cancer. In Study 2 (N = 258), exposure to a pro-conspiracy (vs. anti-conspiracy) content related to cancer treatment was associated with more conspiracy beliefs, less intention to use chemotherapy and more intentions to use unconventional medicines. Exploratory analyses revealed that these effects were conditioned by the credibility of the misinformation. Study 3 (N = 462) replicated these findings using a full experimental design. Exposure (vs. no exposure) to a warning and accuracy prompt, prior to exposure to the pro-conspiracy content, was found to be effective in reducing its credibility and preventing its detrimental effects. These findings corroborate the existence of an effect of conspiracy beliefs.