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Why do animal studies sometimes last longer for drugs intended for long-term use?

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A lab technician wearing protective gloves and face shield lifts a rack of deep-frozen cells from a cryopreservation tank emitting vapor in a laboratory setting. — pharmaceutical industry A technician withdrawing deep-frozen cells for in vitro culture at a laboratory of a German pharmaceutical company.

In the pharmaceutical industry, the duration of animal toxicity studies is directly linked to the intended length of human use for a drug. This practice is grounded in the ethical imperative to prioritize human safety by identifying potential long-term health risks before a medication is widely prescribed.12

When a drug is intended for long-term use—specifically for six months or longer—regulatory requirements mandate extended animal toxicity studies to ensure that chronic exposure does not lead to unforeseen physiological, neurological, or biochemical harm. These studies, which last six months or more, are designed to detect cumulative toxicities that would not appear in shorter, acute, or subchronic tests. Furthermore, if a drug is intended for such long-term use, carcinogenicity studies are generally required to assess the potential for the drug to cause cancer.1

By conducting these longer-duration studies, researchers aim to protect patients from chronic adverse effects, reflecting the industry's responsibility to balance scientific progress with the fundamental ethical principle of "do no harm" to human subjects.12