What is toxicology?

What toxicology studies

Toxicology examines how substances cause harm: the types of adverse effect they produce, the organs or systems affected, and how harm relates to the level and duration of exposure. A central principle is that the dose influences whether and how a substance is harmful — the relationship between exposure and adverse effect is itself a key object of study, mirroring the dose–response thinking in pharmacodynamics. Toxicology overlaps closely with pharmacology: where pharmacology studies a drug’s effects in general, toxicology focuses specifically on the harmful ones.

Preclinical safety testing

In drug development, toxicology provides the preclinical safety evidence required before a candidate can be tested in people. These studies assess effects across single and repeated exposures and examine specific concerns such as effects on reproduction or genetic material. The findings help define a starting point for first-in-human studies and inform what to monitor. Internationally, the design and conduct of these safety studies are shaped by ICH guidelines, and many are performed under Good Laboratory Practice quality standards so that the data are reliable and accepted by regulators such as the FDA.

Toxicology across the lifecycle

Toxicological understanding does not stop at the preclinical stage. It informs the interpretation of adverse effects seen in clinical trials, links to ADME because metabolites can themselves be toxic, and connects to pharmacovigilance, which monitors harms once a medicine is in wide use.

As a discipline, toxicology supplies the safety half of the benefit–risk judgements that run through the whole pipeline, from discovery to post-market surveillance. It describes how harm is studied scientifically and is not advice about the safety of any specific product for any individual.