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.
An antagonist is a drug that blocks the response produced by an agonist. It interacts with the receptor or other component of the effector mechanism, but is devoid of intrinsic activity (ie, the ability to elicit a response upon binding to a receptor).t considers both drug action, which refers to the initial consequence of a drug-receptor interaction, and drug effect, which refers to the subsequent effects. The drug action of digoxin, for example, is inhibition of membrane Na + /K + -ATPase; the drug effect is augmentation of cardiac contractility.