<unk>  occurs when a drug's mechanism of action is<unk> sturbed by the concomitant administration substances such as foods, beverages or other drugs. The cause is often the inhibition of the specific receptors available to the drug, forcing the drug molecules to bind to other non-intended targets which result in an array of side-effects. The term selectivity describes a drug’s ability to target a single receptor, rendering a predictable physiological response. For example, the binding of acetylcholine to muscarinic tracheal smooth-muscle receptors (M3) results in smooth muscle contractions. When free-receptors become occupied by agonists - drugs that bind and activate receptors - and antagonists - drugs that inhibit/block activation -, the opportunity for drugs to target their intended receptor decreases as most receptors are already occupied. Therefore when the amount of free-receptors decreases, the drugs begin binding to other secondary receptors, causing side-effects. Additive drug-drug<unk> s occur when numerous substances are added to the body. These can be synergistic (resulting in a larger effect), or antagonistic (resulting in a lesser effect). For example, consuming both ambien and alcohol (both depressants) influxes the GABAA receptors, resulting in the over-stimulation of sleep-inducing chemicals, resulting in unconsciousness. The risk of a drug-drug<unk>  increases with the number of drugs used. Over a third (36%) of the elderly in the U.S. regularly use five or more medications or supplements, and 15% are at risk of a significant drug-drug<unk> .
Drug interaction
Antibiotic synergy
Tissue stress
Side effect
Electrolyte exclusion effect
Fixed drug reaction
Ischemic compression
Opportunistic infection