I do not think they are considered retro. Interventional studies are widely considered the "golden" standard but they are not perfect and, in many cases, not fe

I do not think they are considered retro. Interventional studies are widely considered the "golden" standard but they are not perfect and, in many cases, not feasible. Like you point out, in many cases, it would not be ethical to perform one ; for example, making people smoke on purpose and then try out smoking cessation interventions on them. "Luckily" though, people usually self-select their selves into these categories.