What are excipients doing in medicinal products?

Medicinal products contain not only active drugs but also other ingredients included for a variety of purposes and collectively known as excipients (from the Latin word excipere, meaning 'to take out or receive'). Prescribers may wrongly overlook or dismiss excipients on the assumption that these are inactive. In reality, such substances are not always inert and may have risks. Here we consider why excipients are present in medicines, their potential unwanted effects, how they are regulated and where to find out more about them.