In this study of community-dwelling older adults, prescription and nonprescription 
medications were commonly used together, with nearly 1 in 25 individuals 
potentially at risk for a major drug-drug interaction. 

Design, Setting, and Participants:  Three thousand five community-residing 
individuals, aged 57 through 85 years, were drawn from a cross-sectional, 
nationally representative probability sample of the United States. In-home 
interviews, including medication logs, were administered between June 2005 and 
March 2006. Medication use was defined as prescription, over-the-counter, and 
dietary supplements used "on a regular schedule, like every day or every week." 
Concurrent use was defined as the regular use of at least 2 medications. 

Results:  The survey response rate was 74.8%.  Eighty-one percent used at least 
1 prescription medication, 42% used at least 1 over-the-counter medication, and 
49% used a dietary supplement. Twenty-nine percent used at least 5 prescription 
medications concurrently; this was highest among men and women aged 75 to 85 
years.  Among prescription medication users, concurrent use of over-the-counter 
medications was 46% and concurrent use of dietary supplements was 52%.  
Overall, 4% of individuals were potentially at risk of having a major drug-drug 
interaction; half of these involved the use of nonprescription medications. These 
regimens were most prevalent among men in the oldest age group and nearly half 
involved anticoagulants.  No contraindicated concurrent drug use was identified. 

Conclusions:   In this sample of community-dwelling older adults, prescription and 
nonprescription medications were commonly used together, with nearly 1 in 25 
individuals potentially at risk for a major drug-drug interaction. 
[Source JAMA. 2008; 300(24):2867-2878.]