Editing Drug interaction (section)

{{short description|Change in the action or side effects of a drug caused}}{{More citations needed|date=November 2023}}[[File:Citrus paradisi (Grapefruit, pink) white bg.jpg|thumb|250px|[[Grapefruit]] juice can act as an enzyme inhibitor, [[Grapefruit–drug interactions|affecting the metabolism of drugs]].]]In [[pharmaceutical sciences]], '''drug interactions''' occur when a drug's [[mechanism of action]] is affected by the [[Concomitant drug|concomitant]] administration of substances such as foods, beverages, or other drugs. A popular example of drug–food interaction is the effect of [[Grapefruit–drug interactions|grapefruit on the metabolism of drugs]]. 

Interactions may occur by simultaneous targeting of [[Drug receptors|receptors]], directly or indirectly. For example, both [[Zolpidem]] and alcohol affect [[GABAA receptor|GABA<sub>A</sub> receptors]], and their simultaneous consumption results in the overstimulation of the receptor, which can lead to loss of consciousness.  When two drugs affect each other, it is a '''drug–drug interaction (DDI)'''. The risk of a DDI increases with the number of drugs used.<ref name="pmid24745854">{{cite journal |vauthors=Tannenbaum C, Sheehan NL |date=July 2014 |title=Understanding and preventing drug–drug and drug–gene interactions |journal=Expert Review of Clinical Pharmacology |volume=7 |issue=4 |pages=533–44 |doi=10.1586/17512433.2014.910111 |pmc=4894065 |pmid=24745854}}</ref> 

A large share of [[Old age|elderly]] people regularly use five or more medications or supplements, with a significant risk of side-effects from drug–drug interactions.<ref>{{cite journal |vauthors=Qato DM, Wilder J, Schumm LP, Gillet V, Alexander GC |date=April 2016 |title=Changes in Prescription and Over-the-Counter Medication and Dietary Supplement Use Among Older Adults in the United States, 2005 vs 2011 |journal=JAMA Internal Medicine |volume=176 |issue=4 |pages=473–82 |doi=10.1001/jamainternmed.2015.8581 |pmc=5024734 |pmid=26998708}}</ref>

Drug interactions can be of three kinds:

* additive (the result is what you expect when you add together the effect of each drug taken independently), 
* [[Synergy#Drug synergy|synergistic]] (combining the drugs leads to a larger effect than expected), or 
* [[antagonism (chemistry)|antagonistic]] (combining the drugs leads to a smaller effect than expected).<ref>{{Cite journal |last1=Greco |first1=W. R. |last2=Bravo |first2=G. |last3=Parsons |first3=J. C. |date=1995 |title=The search for synergy: a critical review from a response surface perspective |journal=Pharmacological Reviews |volume=47 |issue=2 |pages=331–385 |issn=0031-6997 |pmid=7568331}}</ref> 

It may be difficult to distinguish between synergistic or additive interactions, as individual effects of drugs may vary. 

Direct interactions between drugs are also possible and may occur when two drugs are mixed before [[intravenous injection]]. For example, mixing [[thiopentone]] and [[suxamethonium]] can lead to the [[Precipitation (chemistry)|precipitation]] of thiopentone.<ref>{{Cite journal |last1=Khan |first1=Shahab |last2=Stannard |first2=Naina |last3=Greijn |first3=Jeff |date=2011-07-12 |title=Precipitation of thiopental with muscle relaxants: a potential hazard |journal=JRSM Short Reports |volume=2 |issue=7 |pages=58 |doi=10.1258/shorts.2011.011031 |issn=2042-5333 |pmc=3147238 |pmid=21847440}}</ref>