Define briefly drug antagonism ?

(By Dr. Ahmad Najmi, Index Medical College, Indore)
When one drug decrease the action of another drug, they are k/a antagonist.Depending on mechanism involved antagonism may be
1. Physical e.g. charcoal adsorb alkaloids
2. Chemical e.g. Chelating agents complex toxic metals
3. Physiological e.g. Glucagon & insulin on blood sugar
4. Receptor is further divided into competetive & noncompetetive
In competetive type of antagonism, antagonist is chemically similar to agonist & bind to the same site.
In noncompetetive type of antagonism, the antagonist is chemically unrelated to the agonist, bind to a different allosteric site.