What is Synergism?

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  • Written By: Tricia Ellis-Christensen
  • Edited By: O. Wallace
  • Last Modified Date: 21 October 2016
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In medicine, synergism is usually linked to the use of more than one drug at the same time. This can be either positive or negative, or it may have little to no effect. Essentially, the concept of synergy is that things work together to produce a more pronounced effect, and understanding how drugs may interact can either create better treatment or help determine which medicines should not be used together.

There are many drugs that are routinely combined and may work more effectively together than they do apart. Many prescription pain medications that contain drugs like codeine or hydrocodone also contain the common over the counter drug acetaminophen, because opioids combined with it may do more to address pain. Similarly, codeine often gets combined with promethazine in cough syrup, which can help the medicine work better and promote more restful sleep. The cocktail of medications for HIV may also work better together than apart.


Positive synergism exists in numerous other drugs, where one medicine helps the other work more effectively. Alternately, doctors also have lists of medications that don’t seem to interfere with each other. These medicines don’t necessarily work synergistically, but they don’t seem to be dangerous when taken together. For example, many adults with cardiac conditions will take more than two cardiac medicines to deal with the different aspects of their conditions. People, who have complex mood disorders or conditions like depression, might take a standard anti-depressant or anti-convulsant with other medications like anxiolytics or antipsychotics.

The opposite of positive synergism, when drugs enhance their effects so much that they become dangerous, is called negative synergism. There are certain medications that are not typically combined — unless the need is extremely great — because they can prove life threatening. Any drug that has the tendency to suppress breathing usually isn’t mixed with other drugs that can have the same consequence, since the end result might be stopping breathing.

The average opioid pain medicine usually wouldn’t be combined with anti-anxiety drugs, or two opioids might not be used in combination. Selective serotonin reuptake inhibitors (SSRIs), which are common treatment for depression, usually are not added together. Two SSRIs used together can produce so much free serotonin in the system that they cause serotonin syndrome, which is very dangerous.

Some cardiac drugs, like the blood thinner warfarin, interact in one way or another with a very long list of other medications. These medications may either increase or decrease blood levels of warfarin and must be avoided. Actually, warfarin can have a synergistic relationship with many foods too, and people taking this medicine must watch diet and have their blood levels evaluated regularly.

Also related to human health is the synergism that can occur when chemicals like pesticides are mixed. Alone, a single chemical may not pose an issue, but combined with other chemicals it could prove deadly. To avoid these potentially life-threatening reactions, the way chemicals interact with each, whether they’re used for drugs or for other purposes, must be researched and documented.


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