Improving Patient Understanding of Prescription Drug Label
Terry C. Davis, PhD1, Alex D. Federman, MD, MPH2, Pat F. Bass III, MD1, Robert H. Jackson, MD1,
Mark Middlebrooks, Pharm D1, Ruth M. Parker, MD3, and Michael S. Wolf, PhD, MPH4
1Departments of Medicine and Pediatrics, Louisiana State University Health Sciences Center, Shreveport, LA, USA;2Division of General Internal
Medicine, Mount Sinai School of Medicine, New York, NY, USA;3Emory University School of Medicine, Atlanta, GA, USA;4Health Literacy and
Learning Program, Center for Communication in Healthcare, Institute for Healthcare Studies & Division of General Internal Medicine, Feinberg
School of Medicine, Northwestern University, Chicago, IL, USA.
BACKGROUND: Patient misunderstanding of instruc-
tions on prescription drug labels is common and a likely
cause of medication error and less effective treatment.
OBJECTIVE: To test whether the use of more explicit
language to describe dose and frequency of use for
prescribed drugs could improve comprehension, espe-
cially among patients with limited literacy.
DESIGN: Cross-sectional study using in-person, struc-
PATIENTS: Three hundred and fifty-nine adults waiting
for an appointment in two hospital-based primary care
clinics and one federally qualified health center in
Shreveport, Louisiana; Chicago, Illinois; and New York,
New York, respectively.
MEASUREMENT: Correct understanding of each of ten
label instructions as determined by a blinded panel
review of patients’ verbatim responses.
RESULTS: Patient understanding of prescription label
instructions ranged from 53% for the least understood to
89% for the most commonly understood label. Patients
were significantly more likely to understand instructions
day compared to instructions stating times per day (i.e.,
twice) or hourly intervals (89%, 77%, 61%, and 53%,
respectively, p<0.001). In multivariate analyses, dosage
instructions with specific times or time periods were
significantly more likely to be understood compared to
relative risk ratio (ARR) 0.42, 95% Confidence Interval (CI)
0.34–0.52; specific times — ARR 0.60, 95% CI 0.49–0.74).
independent predictors of misinterpreting instructions
(low - ARR 2.70, 95% CI 1.81–4.03; marginal -ARR 1.66,
95% CI 1.18–2.32).
CONCLUSIONS: Use of precise wording on prescription
drug label instructions can improve patient compre-
hension. However, patients with limited literacy were
more likely to misinterpret instructions despite use of
more explicit language.
KEY WORDS: literacy; health literacy; drugs; prescription medications;
labels; patient safety; medication regimens.
J Gen Intern Med 24(1):57–62
© Society of General Internal Medicine 2008
concern1–3. The 2006 Institute of Medicine Report, Preventing
Medication Errors, cited poor patient comprehension and
subsequent unintentional misuse of prescription drugs as a
root cause of medication error, poor adherence, and worse
health outcomes3. A recent study by our research team found
nearly half of primary care patients misunderstood common
dosage instructions on prescription container labels4. Patients
with limited literacy and those taking more medications were
at greatest risk. As patients, particularly the elderly, are taking
an increasing number of prescription drugs, the ability to
accurately interpret medication instructions becomes even
more critical for ensuring proper and safe use5,6.
While limited literacy may impede patient comprehension of
medication dosage instructions, the instructions also may not
be written in the most clear and precise manner7–10. There is
little evidence supporting best practices for writing prescrip-
tion medication dosage instructions to promote patients’
understanding of use. Data from our previous study and
earlier cognitive factors research suggest that less complex
and more explicit dosage instructions might improve patient
understanding4,7,11–15. The purpose of this study was to
evaluate whether the use of more explicit language to describe
the dose and frequency of prescribed drugs could improve
comprehension, especially among patients with limited litera-
cy. We hypothesized that more explicit instructions would
improve patient interpretation, and the association between
literacy and understanding how to take prescribed drugs
would be reduced.
atient misunderstanding of instructions on prescription
drug labels is a medication safety and health literacy
Study participants were adult patients who attended one of
three outpatient primary care clinics in Shreveport, Louisiana,
Received April 28, 2008
Revised August 8, 2008
Accepted October 1, 2008
Published online November 1, 2008
Chicago, Illinois and New York, New York. All of these study
clinics provide care for a large number of indigent patients.
Subject recruitment took place from May to December 2006.
The Shreveport and New York clinics were within a public
university hospital while the Chicago study clinic was a
Federally Qualified Health Center. Institutional Review Boards
at the affiliated institutions (Louisiana State University Health
Sciences Center at Shreveport, Northwestern University,
Mount Sinai School of Medicine) approved this study.
Patients at the three clinics were eligible if they were 18
years of age or older. Research assistants (RA) approached
consecutive patients in each clinic while they were waiting to
see physicians. Patients were excluded from participation if
they reported they had severely impaired vision, hearing
problems, were acutely ill, or did not speak English. A total of
401 patients were approached and 373 consented to the study.
Nine individuals were excluded based on language barriers,
and three were ineligible due to visual impairment. In all, 359
consented to the study (90% response rate).
Selection of Prescription Instructions
We studied instruction labels for three commonly prescribed
medications: glyburide, metformin, and atenolol. Three physi-
cians and one pharmacist identified a typical dose for each
medication, along with variations in the frequency of use for
the drug’s daily administration. Atenolol was written to be
taken once a day, while glyburide and metformin were written
for twice a day. A minimum of three variations of the dosage
instructions were used per drug, ranging from vague to most
explicit. Specifically, frequency of use for the prescribed drug
was presented either as 1) number of times per day (“twice
daily”), 2) hourly intervals (“every 12 hours”), 3) time periods
(“morning”, “evening”), or 4) specific times (“8 A.M.”, “5 P.M.”;
Table 2). A total of ten mock pill bottles were developed based
on these different presentations of dose (number of pills) and
frequency of use (number of times to be taken per day) for the
Structured Interview and Literacy Assessment
After obtaining informed consent, a trained RA administered a
structured interview that lasted approximately 20 minutes and
included a self-report of sociodemographic information (age,
gender, race/ethnicity, and education, number of prescription
medicines taken daily) and a brief literacy assessment. The RA
then showed each patient the ten prescription bottles one at a
time and asked “How would you take this medicine?” The RA
documented patients’ verbatim responses. All patients viewed
the pill bottles in the same order, which was determined by
random assignment. This procedure has been widely used by
this research team to assess patients’ functional understand-
ing of prescription drug instructions and warnings4,7,11.
Patient responses were independently rated as either correct
or incorrect by three general internal medicine attending
physicians from two academic medical centers. Physicians
were blinded to patient information and were trained to follow
stringent coding guidelines previously agreed upon by the
research team7. Correct scores were given only if patients’
responses included both the proper dose (number of pills to be
taken at one time) and frequency of use (number of times drug
is to be taken daily) as stated on the label. For label
instructions that detailed a drug’s frequency using hourly
intervals or time periods, raters followed a predetermined
range of acceptable responses for coding purposes to allow
for some variability in interpretation. Instructions that includ-
ed specific times for taking the medicine had to be precise or
give a very close approximation to be correct. If frequency was
stated using the number of times per day, responses were
correct if either the exact number was reported back, or if
appropriate specific times or time periods (i.e., 8 A.M., noon,
5 P.M.; breakfast, lunch, dinner) were described. If patients’
responses were inaccurate or incomplete in their interpreta-
tion they were scored as incorrect.
Inter-rater reliability between the three physicians coding
the patient responses was very high (Kappa=0.84). Responses
that received discordant ratings between the three reviewers
(n=252) were scored by a panel of one primary care physician
and two behavioral scientists with expertise in health literacy.
Each panel member, blinded to patient information, indepen-
dently coded the responses as correct or incorrect. A consen-
sus ruling was achieved for 91% of responses. A majority rule
was used for the remaining 24 responses.
Literacy Assessment. Patient literacy was assessed using the
Rapid Estimate of Adult Literacy in Medicine (REALM), a
reading recognition test comprised of 66 health related words
16,17. The REALM is the most commonly used test of patient
literacy in medical settings18. Raw scores can be converted into
one of three reading levels: sixth grade or less (0–46), seventh
to eighth (45–60), ninth grade and above (61–66). The REALM
is highly correlated with other standardized reading tests
and the Test of Functional Health Literacy in Adults
All statistical analyses were performed using SAS software
version 9.1 (Cary, NC). Descriptive statistics (percentage, mean
and standard deviation) were calculated for each variable. Chi-
square tests were used to evaluate the association between
sociodemographic characteristics and patient understanding
of each of the ten prescription label instructions. In multivar-
iate analysis, the ten binary repeated responses of correct vs.
incorrect understanding per subject were modeled using a
generalized linear model with a complementary log–log link
function. A generalized estimating equation (GEE) approach
was used to adjust model coefficients and standard errors for
within-patient correlation using PROC GENMOD (SAS Insti-
tute, Cary, NC). Wald 95% confidence intervals were calculated
for adjusted relative risk ratios using the robust estimate of the
standard error as detailed by Liang and Zeger20,21. The final
multivariate model included the variables age, gender, race
(white vs. African American), education, site, and number of
medications currently taken daily. The type of language used
to state frequency of use (times per day, hourly intervals, time
periods, specific times) was entered in the model as the
primary independent variable of interest. The complexity of
the instruction (one tablet a day vs. two tablets twice daily) was
considered to be a potential risk factor to patient understand-
ing and also entered in the analysis as a covariate. Patient
literacy was classified either as low (6th grade and below),
marginal (7th–8th grade) or adequate (9th grade and higher).
Davis et al.: Literacy Medication Labels
In order to examine whether more explicit instructions could
overcome the barrier of limited literacy on patient understand-
ing, an interaction term for literacy and type of language used
in the instruction was included in the final model.
The mean age of patients was 48.4 years (SD=13.7; range 20
to 80 years); 72% were female and 61% were African-Ameri-
can. Approximately half of patients were recruited in Shreve-
port (56%), 25% in New York City, and 19% in Chicago. Twenty
percent of respondents had less than a high school education;
15% were identified as reading at or below a 6th grade level
(low literacy), and 30% were reading at the 7th–8th grade level
(marginal literacy). Patients were currently taking an average
of 2.8 prescription medications (SD=2.9). Low literacy was
associated with older age (p<0.001), African American race (p<
0.001), and less education (p<0.001; Table 1).
Each patient provided interpretations for ten different
instructions for a total of 3,590 responses for the three drugs.
Of these 839 (23%) were coded as incorrect. Seventy-eight
percent of patients misunderstood one or more instructions,
with 37% misunderstanding a minimum of three labels. The
prevalence of incorrectly interpreting one or more label
instructions among patients with adequate, marginal and low
literacy was 71%, 84%, and 93%, respectively (p<0.001). Rates
of correct interpretation were lowest for instructions that
depicted frequency in hourly intervals or the number of times
of day (“Take 1 pill by mouth every 12 hours with a meal”,
“Take two tablets by mouth twice daily”; 53% and 61%,
respectively) and highest for those that used time periods
(“Take 2 pills in the morning and 2 pills in the evening”, “Take 1
pill by mouth every day. Take in the morning”; 89% for both
Patients with low literacy were more likely to misinterpret
seven of the ten instructions compared to those with adequate
literacy (Table 2). Two of three label instructions where literacy
was not significantly associated with correct interpretations
were for atenolol, which had the most basic frequency
schedule (1 tablet a day). No statistically significant differences
in rates of understanding the medication labels were noted by
either age or number of prescription medications currently
taken by patients.
In multivariate analyses, prescription instructions that gave
time periods (morning, evening) or specific times (8 A.M. and
5 P.M.) were significantly less likely to be misinterpreted
compared to those using the number of times per day [twice
daily] (time period — adjusted relative risk ratio (ARR) 0.42,
95% confidence interval (CI) 0.34–0.52; specific times — ARR
0.60, 95% CI 0.49–0.74; Table 3). Frequency of use stated in
hourly intervals (i.e., every 12 hours) was significantly more
likely to be misinterpreted compared to writing frequency as
the number of times per day (ARR 2.87, 95% CI 2.29–3.60).
The reference group was then altered from the previous times
per day to time periods in order to determine if this latter
format significantly improved patient comprehension com-
pared to the use of specific times. Misinterpretation of
instructions was higher with the use of specific times com-
pared to time periods (ARR 1.43, 95% CI 1.19–2.71).
Low and marginal literacy were also statistically significant
independent predictors of misinterpreting instructions (low —
ARR 2.70, 95% CI 1.81–4.03; marginal —ARR 1.66, 95% CI
1.18–2.32). Fewer years of education (< high school, ARR 1.36,
Table 1. Sample Characteristics Stratified by Literacy Level
Characteristic: Literacy levelP
(n = 109)
Age, mean (SD)45.3 (13.0) 51.3
Completed high school/GED
> High school
Number of medications taken
daily, mean (SD)
Study site, %
New York, New York
Table 2. Correct Interpretation of Prescription Medication
Instructions, By Literacy Level
Adequate Marginal Low
(n=195) (n=109)( n =
Atenolol, 50 mg
[Times per day] Take one tablet
by mouth once daily.
[Time periods] Take 1 pill by
mouth every day. Take in the
[Specific times] Take 1 pill by
mouthevery day. Take at 8a.m.
Metformin, 1000 mg
[Hourly intervals] Take 1 pill by
mouth every 12 hours.
[Times per day] Take one tablet
by mouth twice daily.
[Time periods] Take 2 pills by
mouth every day. Take 1 with
Breakfast and 1 with supper.
[Specific times] Take 2 pills by
mouth every day. Take 1 at
8 A.M. and 1 at 5 P.M.
Glyburide, 5 mg
[Times per day] Take two tablets
by mouth twice daily.
[Time periods] Take 2 pills in the
morning and 2 pills in the
[Specific times] Take 2 pills by
mouth at 8 a.m. and 2 pills at
91 92 72<0.001
86 83 760.20
61 51 30 <0.001
88 8478 0.14
8569 74 0.003
71 5733 <0.001
92 8876 0.004
9086 76 0.03
†Bracketed text indicates the classification of language used to state
frequency of drug use
Davis et al.: Literacy Medication Labels
95% CI 1.03–1.77) and greater dose complexity (four tablets
taken per day [glyburide]); ARR 1.47, 95% CI 1.20–1.83) were
also found to be significantly and independently associated
with misinterpretation. The interaction term for literacy and
type of language used to depict drug frequency of use was
included in the final multivariate model; it approached but did
not reach statistical significance (ARR 0.91, 95% CI 0.85–1.01;
Physicians may assume patients can interpret prescription
drug label instructions, yet four out of five patients (79%) in
this study misinterpreted one or more of the ten common
prescription label instructions they encountered. Although
the instructions were brief and of minimal reading difficulty,
rates of patient understanding varied widely across all
literacy levels. More explicit language instructing patients
when to take the medicine using time periods were better
understood compared to instructions that more vaguely
stated the number of times per day or hourly intervals. This
finding is supported by prior research demonstrating that
older adults have greater difficulty interpreting medication
instructions that do not explicitly detail how and when to
take a prescribed medicine13–15.
Labels that instruct patients to take medications “twice
daily” or “every 12 hours” require patients to make additional
mental steps to infer when to take a medicine. For patients
with limited literacy, this adds an unnecessary cognitive
burden, resulting in poorer comprehension12. Despite the use
of more precise instructions, however, comprehension among
those with low literacy skills was still significantly lower than
patients with marginal or adequate literacy skills. This is also
not surprising, as earlier health literacy studies found that
materials with low reading grade levels were likely to improve
comprehension among patients with adequate literacy, but
had only variable success in improving comprehension among
patients with low literacy22.
Interestingly, identifying specific times eachday (8A.M.,5 P.M.)
for administration was a more easily understood instruction
format than stating times per day or hourly intervals. However,
patients were significantly more likely to misinterpret these
instructions compared to those stating time periods in the day
(morning, evening). It is possible that patients do not need such
precision when following medication instructions. Stating
frequency using time periods of day rather than precise times
may better reflect patients’ preference to tailor the implemen-
Table 3. Generalized Estimating Equation (GEE) Model†for Misunderstanding Prescription Medication Label Instructions
ARR 95% CIP
> High school
Completed high school/GED
Number of medications taken daily
Frequency of use
Times per day (once, twice)
Hourly intervals (every 12 hours)
Time period (morning, evening)
Specific times (8 a.m., 5 p.m.)
One tablet a day (atenolol)
Two tablets a day (metformin)
Four tablets a day (glyburide)
RR = relative risk; CI = confidence interval; ARR = adjusted relative risk
†Multivariate ARRs adjusted for site in addition to all variables shown
Davis et al.: Literacy Medication Labels
tation of their drug regimens to their daily schedule. Also of
note, more complex dose regimens requiring patients to take
more pills a day was a significant independent predictor of
misinterpretation of instructions. A prescription requiring a
patient to take four pills a day was 47% more likely to be
misinterpreted than instructions for a ‘one-a-day’ regimen.
Patients with low literacy did not differ significantly from those
with adequate literacy in interpreting instructions to take one
pill a day, or even understanding “Take 2 pills by mouth every
day” and “Take 1 with breakfast and 1 with supper.” Although
the latter instruction involved taking pills two times daily, the
label broke down the instructions for dose and frequency and
provided a context for the time of day.
The limitations to our study should be noted. First, we
investigated patient understanding of different styles of writing
instructions included on the primary label for prescription
medications only. The association between misunderstanding
of these instructions and medication error was not examined.
We also did not study patients’ actual prescription drug-taking
behaviors. Patients’ motivation, concentration and compre-
hension might have been greater if they were reporting on their
own medicine given by their physician for conditions they or
their children actually had14,23,24. Second, since the study
design did not include a chart review, we did not have
information on patients’ health information; in particular
whether they had actual experience with the study medica-
tions. Third, we primarily manipulated the language for
frequency of use; however there were more subtle differences
in word choice and numeric presentation of dose on the
various drug instructions that may also have altered patients’
understanding. Fourth, patients in our study were mostly
socioeconomically disadvantaged individuals from three pri-
mary care clinics in diverse areas of the country. Our sample
addresses those individuals disproportionately affected by
poor health outcomes, and whose health care are targeted for
improvement by Healthy People 201025. Finally, the generaliz-
ability of our findings are further limited by the fact that
patients were predominantly female (an accurate depiction of
the clinic patient populations), and that participation was
limited to patients who spoke English. This was due in part to
criteria for using the Rapid Estimate of Adult Literacy in
Medicine (REALM) as our literacy assessment.
While further improvements might be made in the design of
prescription drug labels, it is likely that patient counseling will
also be needed to address health literacy deficits. Previous
research has found physicians do not commonly review the
instructions when prescribing medications, nor do pharma-
cists routinely verbally counsel patients when filling a pre-
scription26–29. Both the American Medical Association and
American Pharmacists Association recommend provider train-
ing in health literacy communication ‘best practices’29,30. A
highly efficacious approach described in recent cognitive
factors research, known as “implementation intention” might
also aid provider training activities31. This could be a
promising health literacy strategy at the provider level, as it
refers to a process of helping patients visualize exactly how a
prescribed medication will be self-administered within the
context of their own daily routine. As minimal standards exist
to guide physician and pharmacist best practices for writing
and transcribing the dose and frequency of use on label
instructions for patients, both professionals should make it
their goal to be simple, clear and explicit in directing patients
on how to self-administer their medication.
Acknowledgement: The authors are grateful to Mary Bocchini, Kat
Davis, Sumati Jain, Jennifer Webb, Jessica Salazar and Silvia
Skripkauskas. The study was supported in part by internal funding
from the Health Literacy and Learning Program at Northwestern
Conflict Of Interest: None disclosed.
Corresponding Author: Michael S. Wolf, PhD, MPH; Health
Literacy and Learning Program, Institute for Healthcare Studies &
Division of General Internal Medicine, Feinberg School of Medicine,
Northwestern University, 750 N. Lake Shore Drive, 10th Floor,
Chicago, IL 60611, USA (e-mail: email@example.com).
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