Cell Studies vs Animal Studies vs Human Trials

Three levels of evidence

Health research moves through levels. Each answers a different question, and a result at one level does not stand in for the next. This page defines the terms other pages in this section link to. It is information only, not medical advice. The labels it mentions are explained in how we label evidence.

Cell studies

NCI defines "in vitro" as in the laboratory (outside the body), the opposite of in vivo. [1] A cell culture is the growth of cells in the laboratory, and it may be used to test new drugs and in research. [2] An organoid is a three-dimensional, mini-organ-like structure grown from a person's tumor cells or stem cells, which closely mimics the structure and some functions of human tissue. [3] Organoids are a more detailed lab model, but they are still a lab model.

Cell work is cheap, fast and useful for narrowing down ideas. Its limits are simple: a dish has no digestion, no blood flow, no immune system and no years of exposure. A substance that affects cells in a dish may never reach them in a body at that strength.

Animal studies

"In vivo" means in the body. [4] An animal model is an animal with a disease the same as or like a human disease, used to study how disease develops and to test new treatments before they are given to humans. [5] The FDA describes preclinical work, in vitro and in vivo, as how researchers find out whether a drug could cause serious harm before it is tested in people. [6]

Animals differ from people in size, metabolism and biology. A systematic review compared animal experiments with human trials for interventions whose effects in people were already clear. Corticosteroids showed benefit in animal models of head injury (pooled odds ratio for adverse functional outcome 0.58) but not in clinical trials. Tirilazad reduced infarct volume by 29% in animal stroke models yet was associated with a worse outcome in patients. [7] The authors suggest the mismatch may be due to bias or to animal models that fail to mimic the disease adequately. [7] That review also found cases that did agree, such as the bone-density effect of alendronate, so the point is not that animal work is useless. It is that agreement cannot be assumed. [7]

Human trials

Clinical trials are research studies that test a medical, surgical or behavioral intervention in people, and they are the primary way researchers determine whether a new treatment or prevention approach is safe and effective. [8] The FDA states that preclinical research is not a substitute for studies of how a drug interacts with the human body. [9] Human studies come in stages, explained in clinical-trial phases explained.

Not every human study is a trial. Observational studies do not test an intervention. They may help identify new treatments or prevention strategies to test in clinical trials. [8] See observational studies and confounding.

Reading the wording

Even in people, check what was measured. A blood marker is not the same as how someone feels or lives. [10] And small trials can overstate effects: across 93 meta-analyses, treatment effects averaged 48% larger in trials with fewer than 50 patients than in trials of 1,000 or more. [11]

What this means for wellness claims

Cell and animal findings are a starting point, so we do not transfer them to people on this site. When a page says what a compound "does", we say in what: cells, animals or humans. For the full path from lab to clinic, see discovery vs clinical application and mechanism vs demonstrated benefit.