First-in-human (FIH) trials mark the first time a new drug or medical device is given to humans — a critical step bridging preclinical work and broader clinical testing. FIH trials primarily aim to assess safety, tolerability, pharmacokinetics, and dosage, often using small cohorts of healthy volunteers. Common designs are single-ascending dose (SAD) studies, where one dose is given then increased in successive groups, and multiple-ascending dose (MAD) studies, where repeated doses are administered over time. Well-designed FIH trials gather early data on how the investigational product behaves in humans, enabling developers to make informed decisions about further clinical phases while minimizing risks for participants.