What is an in vivo study?

Scientist watching mice in laboratory
Scientist watching mice in laboratory. Adam Gault/OJO Images/Getty Images

Definition: In vivo comes from the Latin term "in life." The term refers to studies of biological properties that are performed inside a living organism. When contrasted with in vitro ("in glass") studies, which are done inside a test tube, in vivo studies allow scientists to look at scientific and medical questions within the context of a living organism. Unfortunately, this makes them far more expensive, and often more difficult, than in vitro studies.

However, there are some questions that can only be fully addressed by looking at them in the context of a living organism.

Many STD research studies are in vivo studies. Although early research on STD treatments may be done in test tubes and cell cultures, it's impossible to know how well these treatments will work until and unless they're tested in first animals and then humans. This is true for a number of reasons. First, medications that work in a lab environment don't necessarily work the same way in an organism. However, even if they do, behavior plays a large role in how effective drugs are in the real world. Medications that are hard to take or have significant side effects may cause problems with compliance. Therefore, even when drugs work perfectly in an early trial they may not do nearly as well in the real world.

Not all human subject research is thought of as in vivo research.

Usually the term refers to testing a substance in a human, rather than simply looking at behaviors. For example, understanding how testing works also requires human studies, but not necessarily studies that are thought of as in vivo research. How people choose to test, how doctors behave around testing, and in what situations different tests are most appropriate are all subjects for investigation, but don't necessarily get categorized as in vivo studies, even though they technically are.

Therefore, while clinical trials of medications are discussed as in vivo research, studies focusing on behaviors generally are not.

In the end, in vivo is a term of art that is predominantly used as a way to distinguish human and animal trials from in vitro research. There is a much higher level of complexity in these studies, which is useful to recognize when comparing and contrasting results and interpretations. It's important for early testing that a medication works in vitro, but it says little to nothing about what is going to happen when an organism is treated with the same drug. It's not yet, and may never be, possible to model all the biochemical and physical systems of a living organism, and until it is,in vivo research will remain indispensable.

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