Bioavailability plays an essential role in determining a drug’s efficacy and safety. It is influenced by multiple factors, including the route of administration, drug solubility, metabolism, and individual patient characteristics. Measuring bioavailability through pharmacokinetic studies is vital for optimising drug formulations and dosing regimens. Understanding and improving bioavailability remains a critical challenge in drug development, as enhancing it can significantly improve therapeutic outcomes and reduce drug doses, ultimately benefiting both patients and healthcare providers. Drug delivery systems are integral to modern medicine, providing ways to improve drug efficacy, reduce side effects, and enhance patient compliance. Advances in nanotechnology, targeted delivery, and biodegradable systems offer new possibilities for treating a wide range of diseases. However, ongoing research and innovation are essential to overcome current challenges and continue improving drug delivery technologies.