Experimental research involving new drugs, environmental exposures, or other chemicals or interventions will occur in one of three environments: in a human, in a non-human animal or in a petri dish, test tube, beaker or other environment outside a living multi-celled organism. An “in vitro” experiment occurs outside of a living multi-celled organism whereas an “in vivo” experiment occurs in a human or other animal. These terms are important to know because studies may not clearly explain the experimental setting beyond using in vitro and in vivo. A newer term is in silico, which refers to experiments conducted using a computer, such as modeling, simulation, or gene sequencing.
Deeper dive
Typically, anything not involving a living multi-celled organism is preclinical research, used to show proof of concept or to help generate hypotheses for what might be seen in non-human animals. Animal research also usually comprises preclinical research, though research outside and inside non-human animals also occurs in environmental health research to better understand the effects of substances found in the environment. Some studies, however, involve a combination of settings. Researchers might conduct an epidemiological study on humans and then use what they find to conduct a series of experiments in a petri dish or test tube and/or non-human animal. Or, they may conduct a series of progressive experiments that start with an in vitro setting and progress to in vivo experiments in a non-human animal and then in a human.