In ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other. It compares with mutualism, in which both organisms benefit, amensalism, where one is harmed while the other is unaffected, and parasitism, where one benefits while the other is harmed.n ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other. It compares with mutualism, in which both organisms benefit, amensalism, where one is harmed while the other is unaffected, and parasitism, where one benefits while the other is harmed.
Drug interactions also may occur when two drugs that have similar (additive) effects or opposite (canceling) effects on the body are administered together. For example, there may be major sedation when two drugs that have sedation as side effects are given, for example, narcotics and antihistamines.
Strictly speaking, agonist & antagonist refer to the action of a molecule at a receptor. An agonist molecule produces the same effect as whatever molecule normally binds to that receptor. An antagonist molecule blocks the effects of the molecule that normally binds to that receptor. An inverse agonist produces the opposite effect to the molecule that normally binds to a receptor.