In pharmacology, the term ceiling effect refers to the property of increasing doses of a given medication to have progressively smaller incremental effect (an example of diminishing returns). Mixed agonist-antagonist opioids, such as nalbuphine, serve as a classic example of the ceiling effect; increasing the dose of a narcotic frequently leads to smaller and smaller gains in relief of pain. In many cases, the severity of side effects from a medication increases as the dose increases, long after its therapeutic ceiling has been reached.
The term is defined as "the phenomenon in which a drug reaches a maximum effect, so that increasing the drug dosage does not increase its effectiveness."[1] Sometimes drugs cannot be compared across a wide range of treatment situations because one drug has a ceiling effect.
Sometimes the desired effect increases with dose, but side-effects worsen or start being dangerous, and risk to benefit ratio increases. This is because of occupation of all the receptors in a given specimen.