Polypharmacy, part 3. Online drug interaction checkers to assess side effects.

The Bottom Line

  • There are a number of online drug interaction databases available. There are some problems with using only these databases to identify interactions.
  • You should always ask your doctor or pharmacist to confirm whether the multiple medications you are taking put you at risk for interactions.

In Part 1 we identified that polypharmacy really means you are taking at least 3 to 5 different medications (including vitamins, food supplements and herbs). In Part 2 we discussed how our bodies affect the medications (pharmacokinetics) and medications affect our bodies (pharmacodynamics). Taking multiple medications increases the risk of experiencing interactions and side effects. We also learned that the benefit/risk profile of medications changes with age. 

In Part 3 we discuss when polypharmacy can be a risk to your health. 

Can we know ahead of time if we are at risk for interactions and side effects?

We learned in Parts 1 and 2 of this blog that taking multiple medications may increase our risk of experiencing interactions. Sometimes drug interactions can be harmful to our well-being and we don’t even know about it. Many consumers want to know if there is a way to find out about possible interactions ahead of time.

In fact there are many online resources and electronic applications (Apps) to help you, or the pharmacist, or the doctor identify drug interactions. These online resources are known as “interaction databases” because they check for ways in which drugs might affect you when they are combined. Even though many programs are available to download from the internet for anyone to use, double checking your situation with more than one source is helpful when using these interaction databases.  You should always talk to a healthcare provider to confirm whether your drug regimen may be associated with the risk of a drug interaction.  The advantage of having a professional review your medications is that it gives the person an opportunity to ask questions. It also gives you an opportunity to talk about any additional concerns which are not really captured by the interaction databases (such as, what is the best time to take the medications). 

What does the research show us about polypharmacy?

A good study(1) looked at the accuracy of drug interactions in intensive care unit (ICU) settings using three different types of online interaction database programs. The different software evaluated in this study included:

  1. Drug Interaction Checker (DIC) offered by Medscape, 
  2. Drug-Reax (DR) offered by Micromedex,  
  3. Lexi-Interact (LI) offered by Lexi-Comp. 

This study found that the DR and LI programs showed a good ability to correctly identify the patients with a drug interaction (this is called appropriate ‘sensitivity’). The programs also showed good ability to identify those patients without a drug interaction (this is called appropriate ‘specificity’). So both these software programs available to us on the internet did a good job of identifying potential drug interactions. DIC is offered for free, while LI and DR need paid subscriptions. Other studies have evaluated other interaction databases and these include:

  1. Micromedex, 
  2. Epocrates, 
  3. Lexi-Comp, 
  4. Stockleys Drug interactions and 
  5. Clinical Pharmacology 

These interaction databases also perform well in specificity, sensitivity, ease of use, and completeness depending on the medication interaction examined (2-8). 

A recent study did a good job of selecting and comparing general online interaction database programs; this study compared different features and found that paid software was better than free software (9). 

What are some important things to know about polypharmacy?

The challenge with all these drug interaction checkers is that it may be difficult to apply the results to your specific situation. While there are many studies comparing drug interaction software, it is difficult to choose one product that is best. This is because each study compares interaction database programs based on one or more specific situations which may not be your personal situation.

Another problem is that the programs that check for interactions are based on other studies that record any side effects people may have with a medication. Some of these studies used to describe a drug interaction may be based on very few people or based on studies using healthy volunteers instead of people who have the health condition. 

What is the bottom line about polypharmacy?

As we noted previously, double checking your situation with more than one source is helpful when using these interaction databases. You should always talk to a healthcare provider to confirm whether your medications may be associated with the risk of a drug interaction or side effect.

This four-part series of blog posts explores various aspects of polypharmacy. Part 1 defined the issue. In Part 2, we discuss how aging changes the way our body responds to medications, including when taking multiple medications. Part 3 looks at online drug interaction checkers. Part 4 examines medication reviews.

Get the latest content first. Sign up for free weekly email alerts.
Author Details
Author Details


  1. Reis AM, Cassiani SH. Evaluation of three brands of drug interaction software for use in intensive care units. Pharm World Sci 2010 Dec;32(6):822-8.
  2. Mouzon A, Kerger J, D'Hondt L, Spinewine A. Potential interactions with anticancer agents: a cross-sectional study. Chemotherapy 2013;59(2):85-92.
  3. Vonbach P, Dubied A, Krahenbuhl S, Beer JH. Evaluation of frequently used drug interaction screening programs. Pharm World Sci 2008 Aug;30(4):367-74.
  4. Barrons R. Evaluation of personal digital assistant software for drug interactions. Am J Health Syst Pharm 2004 Feb 15;61(4):380-5.
  5. Clauson KA, Polen HH, Marsh WA. Clinical decision support tools: performance of personal digital assistant versus online drug information databases. Pharmacotherapy 2007 Dec;27(12):1651-8.
  6. Clauson KA, Marsh WA, Polen HH, Seamon MJ, Ortiz BI. Clinical decision support tools: analysis of online drug information databases. BMC Med Inform Decis Mak 2007;7:7.
  7. Perkins NA, Murphy JE, Malone DC, Armstrong EP. Performance of drug-drug interaction software for personal digital assistants. Ann Pharmacother 2006 May;40(5):850-5.
  8. Hoody DW, Beckett CF, Zielenski C, Moore GD. Quality of drug information database research for clinical decision support. Int J Clin Pharm 2011 Aug;33(4):599-602.
  9. Polen HH, Zapantis A, Clauson KA, Jebrock J, Paris M. Ability of online drug databases to assist in clinical decision-making with infectious disease therapies. BMC Infect Dis 2008;8:153.

DISCLAIMER: These summaries are provided for informational purposes only. They are not a substitute for advice from your own health care professional. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the McMaster Optimal Aging Portal (info@mcmasteroptimalaging.org).

Many of our Blog Posts were written before the COVID-19 pandemic and thus do not necessarily reflect the latest public health recommendations. While the content of new and old blogs identify activities that support optimal aging, it is important to defer to the most current public health recommendations. Some of the activities suggested within these blogs may need to be modified or avoided altogether to comply with changing public health recommendations. To view the latest updates from the Public Health Agency of Canada, please visit their website.