text: A receptor agonist is a chemical that binds to a receptor with the end result of directly inducing a conformational change in the bound receptor and activating a downstream effect. Some common examples are opium derivates, such as heroin and Toll-like receptor agonists. Heroin functions in this manner, along with other opioids, when bound to µ-opioid receptors. Opioids' manner of action are both concentration- and receptor-dependent, which provides a key difference between agonists and partial agonists. Another example is insulin, which activates cell receptors to instigate blood glucose uptake.