A study (usually a clinical trial) in which the investigators actively intervene/experiment to test a hypothesis (e.g., the effect of a treatment or intervention on a health- or disease-related outcome).

Conclusions of intervention studies (e.g., randomized controlled trials) can be inaccurate when they try to transfer effects of an intervention (e.g., a high-dose micronutrient therapy) seen in patients or vulnerable groups (e.g., smokers) to consumers using a particular factor in the interest of prophylaxis (e.g., taking fortified foods and/or dietary supplements to prevent micronutrient deficiency).