INTRODUCTION
Polypharmacy is a recognised patient 
safety risk among older adults.1,2 Although 
standard definitions of polypharmacy do 
not generally include herbal medicinal 
products (HMPs) and dietary supplements, 
they increase the risk of adverse drug 
events through potential interactions.3–5 
Use of herbal medicines and dietary 
supplements by older adults is common.6–10 
Also, medication-related problems are 
higher among older adults because of 
comorbidities and reduced clearance of 
pharmacologically active compounds.11
A recent systematic review12 established 
that concurrent use of prescription drugs 
and HMPs is substantial among older 
adults, with potential interactions from 
some herb–drug combinations such as 
garlic–aspirin and ginseng–warfarin. 
However, the only available UK study on 
this issue among older adults13 is nearly 
15 years old, included people aged 
≥50 years, and relied on a self-selected 
sample from a magazine’s readership.
The aims of the study were to establish 
prevalence, and to identify patterns and 
potential herb–drug interactions from 
concurrent use of prescription drugs, 
HMPs, and dietary supplements among UK 
community-dwelling older adults.
METHOD
A cross-sectional survey was conducted 
using self-administered questionnaires 
between January and April 2016. Data were 
from a purposive sample of community-
dwelling older adults registered at two 
general practices in South East England. 
Practice A was a small village practice 
in Essex, with a predominantly white 
population and about 19.5% aged ≥65 years. 
Practice B was a large urban practice in 
Haringey, North London, with a sizeable 
black, Asian, and minority ethnic (BAME) 
population, of up to 9% aged ≥65 years.
Informed by findings from a systematic 
review on concurrent use of HMPs with 
prescription drugs,12 the questionnaire 
covered demographics, prescription 
drugs, HMPs, and dietary supplements not 
prescribed by the GP, the rationale for 
taking them, and how often. Participants 
were also asked about side effects and 
perceived benefits of medicines and/or 
HMPs (further information is available from 
the authors on request).
As no consistent terms exist for HMPs, 
some examples of common HMPs were 
included to show participants the possible 
breadth of responses. The questionnaire 
was piloted among 15 community 
dwelling older adults and, following minor 
TB Agbabiaka, MSc, MPH, research degree 
student, Centre for Research in Public Health 
and Community Care (CRIPACC), University of 
Hertfordshire, Hatfield; evidence & evaluation 
lead, patient safety, Medical Directorate, NHS 
Improvement, London. NH Spencer, PhD, 
reader in applied statistics, Hertfordshire 
Business School, University of Hertfordshire, 
de Havilland Campus, Hatfield. S Khanom, 
MRPharmS, patient safety policy lead (primary 
care), Medical Directorate, NHS Improvement, 
London. C Goodman, PhD, RN, FQNI, professor 
of health care research, CRIPACC, University of 
Hertfordshire, Hatfield. 
Address for correspondence
Taofikat Agbabiaka, Centre for Research in 
Public Health and Community Care (CRIPACC), 
University of Hertfordshire, Hatfield AL10 9AB, 
UK.
Email: t.b.agbabiaka@herts.ac.uk
Submitted: 8 May 2018; Editor’s response:
2 June 2018; final acceptance: 8 July 2018.
©British Journal of General Practice
This is the full-length article (published online 
25 Sep 2018) of an abridged version published in 
print. Cite this version as: Br J Gen Pract 2018; 
DOI: https://doi.org/10.3399/bjgp18X699101
Prevalence of drug–herb and drug–supplement 
interactions in older adults: 
a cross-sectional survey 
Taofikat B Agbabiaka, Neil H Spencer, Sabina Khanom and Claire Goodman
Research
Abstract
Background 
Polypharmacy is common among older adults, 
with increasing numbers also using prescription 
drugs with herbal medicinal products (HMPs) 
and dietary supplements. There is no reliable 
evidence from the UK on concurrent use of 
HMPs and dietary supplements with prescription 
drugs in older adults.
Aim
To establish prevalence of concurrent 
prescription drugs, HMPs, and dietary 
supplements among UK community-dwelling 
older adults and identify potential interactions.
Design and setting
Cross-sectional survey of older adults registered 
at two general practices in South East England.
Method
A questionnaire asking about prescription 
medications, HMPs, and sociodemographic 
information was posted to 400 older 
adults aged ≥65 years, identified as taking 
≥1 prescription drug. 
Results
In total 155 questionnaires were returned 
(response rate = 38.8%) and the prevalence of 
concurrent HMPs and dietary supplements with 
prescriptions was 33.6%. Females were more 
likely than males to be concurrent users (43.4% 
versus 22.5%; P = 0.009). The number of HMPs 
and dietary supplements ranged from 1 to 8, 
(mean = 3, median = 1; standard deviation = 1.65). 
The majority of concurrent users (78.0%) used 
dietary supplements with prescription drugs. 
The most commonly used dietary supplements 
were cod liver oil, glucosamine, multivitamins, 
and vitamin D. Others (20.0%) used only HMPs 
with prescription drugs. Common HMPs were 
evening primrose oil, valerian, and Nytol Herbal® 
(a combination of hops, gentian, and passion 
flower). Sixteen participants (32.6%) were at risk 
of potential adverse drug interactions. 
Conclusion
GPs should routinely ask questions regarding 
herbal and supplement use, to identify and 
manage older adults at potential risk of adverse 
drug interactions.
Keywords
dietary supplements; general practice; 
herb–drug interactions; herbal medicine; 
polypharmacy.
1  British Journal of General Practice, Online First 2018
amendments, the questionnaire consisted 
of 18 questions and took between 20 to 
30 minutes to complete.
Sample size calculation and sampling
The sample size was based on previous 
research evidence that up to 50% of 
older adults use HMPs.14–16 To achieve a 
confidence interval (CI) of 95% and ±7.5% 
accuracy, a power calculation (using 
G*Power version 3.1.9.2) gave the total 
sample size required as 171 responders 
(using the worst-case scenario of actual 
proportion being 50%). 
Purposive sampling17,18 was used to obtain 
a sample of older adults registered at two 
general practices, in Essex and Haringey. 
Participants had to be ≥65 years, using at 
least one prescription drug, and able to 
consent. Terminally ill patients, patients 
with dementia, or patients assessed as 
lacking capacity were excluded. 
To account for attrition from low 
responses, which are common with mailed 
surveys, 200 participants who met inclusion 
criteria were randomly selected from a list 
of patients in each of the two practices. 
Practice administrators posted study packs 
(a letter of invitation addressed personally to 
the patient, participant information sheets 
[PIS], the questionnaire, and a reply-paid 
envelope) to selected patients. Reminder 
letters were sent after 2 weeks. If there was 
no reply, new study packs were sent to all 
non-responders. 
Data analysis
Responders were defined as ‘concurrent 
users’ if they reported using HMPs or 
dietary supplements. Anonymised data 
were recorded and double checked; 
discrepancies were corrected and analysed 
using SPSS (version 23.0). Descriptive 
statistics were calculated to summarise 
the sample. Using Fisher’s exact test, 
associations between concurrent use 
and demographic factors, such as sex, 
educational qualifications, and living 
arrangements, were tested. Statistical 
significance was measured at 5% level.
Potential interactions between 
combinations of prescription drugs, HMPs, 
and dietary supplements were assessed using 
Stockley’s Herbal Medicines Interactions 
(https://about.medicinescomplete.com/
publication/stockleys-herbal-medicines-
interactions-2/). Stockley’s Herbal Medicines 
Interactions is a comprehensive evidence 
database. Information regarding potential 
interactions between herbal medicines 
(including nutritional supplements and 
some food) and conventional medicines 
are expertly assessed with practical advice 
provided and regularly updated. 
Interactions are rated on three criteria: 
whether action is required to address 
the interaction (action); likely effect of the 
interaction on the patient if unmanaged 
(severity); and weight of available evidence 
regarding the interaction (evidence). Based 
on these criteria, drug–herb or drug–
supplement combination is described 
by one of five outcomes ranging from 
no interaction, doubt about outcomes, 
potentially hazardous outcomes, significant 
hazard, and life-threatening outcomes.
All drug–herb and drug–supplement 
combinations were assessed and rated for 
potential interactions by one author and 
double checked by a second author who is a 
registered pharmacist. Any disagreements 
on rating were resolved through discussion.
RESULTS
Table 1 shows sociodemographic 
characteristics of the 149 responders 
included in the final analysis (six responders 
were excluded for not providing information 
on medications). A power calculation based 
on 80% power and significance level of 5% 
for a two-tailed test showed that a sample 
of 128 (64 in each group) was sufficient 
to detect medium standardised effect 
size, and thus the results are unaffected 
by the shortfall in the desired number of 
responders. 
Of these 149 responders, 76 (51.0%) 
were female and 71 (47.7%) were 
male; two participants did not indicate 
gender. The majority (106; 71.1%) were 
aged 65–74 years; none were ≥95 years. 
About half of participants (73; 49.6%) lived 
with a partner or spouse, whereas 31.3% 
lived alone. Most responders identified as 
white (126; 85.7%), with 15 (10.1%) black or 
black British and only one Asian or Asian 
British.
How this fits in
Older adults use herbal medicinal products 
(HMPs) and dietary supplements with 
prescription drugs to manage chronic 
conditions and to maintain health. The use 
of HMPs and dietary supplements with 
prescription drugs among older adults 
is under-researched. Concurrent use 
of HMPs and dietary supplements with 
warfarin, statins, and anti-inflammatory 
drugs is common among UK older adults. 
One in three concurrent users is at risk of 
a potential herb–drug or supplement–drug 
interaction.
British Journal of General Practice, Online First 2018  2 
There was almost an even split in 
educational level between responders: 
70 (46.9%) with further education after 
secondary school and 77 (51.7%) with no 
education beyond secondary school. Only 
one participant, a concurrent user, had a 
clinical background in nursing.
Prevalence and pattern of concurrent use 
Approximately one-third of responders 
reported concurrent use of HMPs and 
dietary supplements with prescribed 
medications in the last 12 months. The 
prevalence of concurrent use is thus 33.6%.
Females were more likely than males to 
be concurrent users (43.4% versus 22.5%, 
P = 0.009). There is little difference between 
groups that had or had no further education 
with each having about one-third reporting 
concurrent use. Similarly, there were 
little differences between the categories 
of living arrangements. Those living with 
children reported somewhat lower levels of 
concurrent use but this was not statistically 
significant.
Concurrent users (n = 50) reported 
55 herb–drug and supplement–drug 
combinations. The number of HMPs and 
dietary supplements ranged from 1 to 8, 
mean value of 3 (standard deviation = 1.65, 
median = 1). 
All responders were taking 
≥1 prescription drugs on a regular basis, 
range 1 to 18 (median = 3). A total of 180 
different types of prescription drugs were 
reported by 149 participants (mean = 3.96, 
standard deviation = 2.52). The most 
reported drug classes were statins (69; 
46.3%), beta-blockers (26; 17.4%), calcium 
channel blockers (23; 15.4%), non-steroidal 
anti-inflammatory drugs (NSAIDs) (19; 
12.7%), biguanides (18; 12.1%), angiotensin-
converting enzyme (ACE) inhibitors (18; 
12.1%), and proton pump inhibitors (18; 
12.1%).
Ten concurrent users (20.0%) used 
only HMPs with prescriptions. Thirty-six 
different herbs (used either singly or as a 
combination product) were reported. The 
most commonly used HMPs were evening 
primrose oil, valerian, Nytol Herbal® (a 
combination of hops, valerian, gentian, and 
passion flower), and garlic (Figure 1). 
The majority of concurrent users (39; 
78.0%) were taking dietary supplements, 
including vitamins and minerals. The 
most combined dietary supplements were 
cod liver oil, glucosamine, multivitamins, 
and vitamin D (Figure 2). Of the 50 
concurrent users, 13 (26.5%) reported 
using both HMPs and dietary supplements 
concurrently with prescription drugs: 
38.8% of concurrent users used ≥3 HMPs 
or dietary supplements concurrently with 
prescription drugs.
Potential interactions between HMPs, 
dietary supplements and prescription 
drugs
Just over half of the 55 herb–drug and 
supplement–drug combinations (n = 28, 
50.9%) were assessed as ‘no interaction’ 
or ‘no interaction of clinical significance’. 
However, 21 combinations were categorised 
as interactions with ‘doubts about 
the outcome of concurrent use’. Three 
combinations were rated as ’potentially 
hazardous’ and three of ‘significant hazard’ 
(Box 1). 
The HMPs implicated in the potential risk 
for interaction include:
• flaxseed;
• evening primrose oil;
• St John’s wort;
• peppermint; 
• senna;
Table 1. Demographics of concurrent users and non-concurrent users 
(n = 149)
 Concurrent users  Non-concurrent users  
Demographics n = 50 (%) n = 99 (%) Total P-valuea
Age group, years 
65–74 37 (34.9) 69 (65.1) 106 (100) 0.729 
75–84  11 (33.3) 22 (66.7) 33 (100)  
85–94  2 (20.0) 8 (80.0) 10 (100) 
Sex  
Male 16 (22.5) 55 (77.5) 71 (100) 0.009b 
Female  33 (43.4) 43 (56.6) 76 (100)  
Not specified 1 (50.0) 1 (50.0) 2 (100)
Ethnic background  
White  40 (31.7) 86 (68.3) 126 (100) 0.184 
Asian or Asian British 1 (100.0) 0 (0.0) 1 (100)  
Black or black British 5 (33.3) 10 (66.7) 15 (100)  
Mixed or multiple background 1 (33.3) 2 (66.7) 3 (100)  
Other ethnic group 2 (100.0) 0 (0.0) 2 (100)  
Not specified 1 (50.0) 1 (50.0) 2 (100)
Further education   
Yes 24 (34.3) 46 (65.7) 70 (100) 0.862 
No  25 (32.5) 52 (67.5) 77 (100)  
 1 (50.0) 1 (50.0) 2 (100)
Living arrangement 
Alone 17 (37.0) 29 (63.0) 46 (100) 0.929 
With partner or spouse 26 (35.6) 47 (64.4) 73 (100)  
With partner or spouse and children 4 (26.7) 11 (73.3) 15 (100)  
With children  2 (28.6) 5 (71.4) 7 (100)  
Otherc 1 (20.0) 4 (80.0) 5 (100)  
Not specified – 3 (100) 3 (100)
aFisher’s exact test. bStatistically significant (P<0.05). cSuch as living with friends or relatives.
3  British Journal of General Practice, Online First 2018
• Echinacea;
• hawthorn;
• green tea; and
• ginkgo. 
The five dietary supplements implicated 
are:
• glucosamine;
• cod liver oil;
• omega 3 fish oil;
• calcium carbonate; and 
• a multivitamin. 
A majority of the identified interactions 
involved potential alterations in the 
concentration or effect of the prescription 
drugs, including calcium channel blockers, 
HMG-CoA reductase inhibitors (statins), 
and aspirin. The seven herb–drug and 
supplement–drug interactions assessed 
as having the potential for hazardous 
outcomes relate to increase in blood 
glucose concentrations, risk of bleeding, 
and reduced efficacy or bioavailability of the 
prescription drug.
DISCUSSION
Summary
Almost one-third of older adults (33.6%) in 
this study’s sample were using an HMP or 
supplement concurrently with prescription 
drugs. About one in three concurrent users 
was at risk of a potential herb–drug or 
supplement–drug interaction. If applied 
to the UK population that would mean 
1.3 million older adults in the UK are at 
risk of at least one potential herb–drug or 
supplement–drug interaction. Importantly, 
six combinations (Box 1) have potential for 
hazardous outcome or significant hazard.
Strengths and limitations
To the authors’ knowledge, this is the 
first UK study in over 10 years assessing 
concurrent use of prescriptions, HMPs, and 
dietary supplements among older adults.13 
The study participants were community-
dwelling older adults recruited from 
general practices; previous UK studies 
have researched patients with cancer,19 
diabetes,20,21 and pregnant women.22 
A response rate of 39% is disappointing 
but high for a study of this kind and enough 
to provide credible findings. Examples 
of HMPs and dietary supplements were 
included in the questionnaire. It is possible 
that some participants did not consider 
products such as garlic or ginger used for 
medicinal purposes as HMPs and did not 
report them.
Comparison with existing literature
The prevalence of concurrent prescription, 
HMPs, and supplement use among older 
adults varies from country to country, 
between 9% and 88.3%.23–33 The prevalence 
of 33.6% reported in this study is similar 
to studies in North America.23 However, 
lower prevalence of 15%27 and 22.8%28 were 
reported in two other US studies. Variation 
in prevalence could be explained by different 
definitions and inclusion criteria for HMPs 
and level of detail required about HMPs. 
Not all studies focused exclusively on older 
people and some were more successful in 
Figure 1. HMPs most frequently used concurrently with 
prescription by UK older adults. Percentages sum to 
more than 100% as individuals could report more than 
one HMP.
Ev
en
ing
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im
ro
se
 oi
l
0
1
2
3
N
um
be
r 
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 r
ep
or
ts 4
5
6
5 (10%)
4 (8%) 4 (8%)
3 (6%)
2 (4%) 2 (4%) 2 (4%) 2 (4%) 2 (4%)
Va
le
ria
n
Co
m
bin
at
ion
 of
 ho
ps
, v
ale
ria
n,
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nt
ian
, p
as
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n f
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we
r
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ac
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am
on
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al 
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an
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 Jo
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5
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15
20
25
N
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of
 r
ep
or
ts
23 (47%)
15 (31%)
10 (20%)
7 (14%)
3 (6%) 3 (6%) 3 (6%)
2 (4%) 2 (4%) 2 (4%)
Co
d/
om
eg
a 3
co
d l
ive
r o
ils
Gl
uc
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am
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(in
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 va
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 fis
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C
Figure 2. Supplements that are most frequently used 
concurrently with prescription by UK older adults. 
Percentages sum to more than 100% as individuals 
could report more than one HMP.
British Journal of General Practice, Online First 2018  4 
recruiting people from BAME backgrounds.
Another possible explanation for 
discrepancies in prevalence of concurrent 
use in this study and those in the literature 
may be problem of recall. Some studies 
asked participants to recall products using 
self-completed questionnaires.13,28–30,34 
Others interviewed face-to-face, checked 
Box 1. Evaluation of potential interactions from HMPs, dietary supplements, and prescription drugs
 Prescription medicine  
HMPs/dietary supplement [number of patientsa] Possible interactionsb
HDI category: Significant hazard, dosage adjustment or close monitoring is needed
Bonecal Levothyroxine  The efficacy of levothyroxine has been reduced by calcium carbonate. Calcium acetate and calcium 
(Pharmanutra)  citrate reduced levothyroxine absorption in pharmacokinetic studies
Peppermint Lansoprazole Antacids may compromise the enteric coating of some commercially available peppermint oil capsules.  
  H2-receptor antagonists and proton pump inhibitors may interact similarly
St John’s wort Amlodipine St John’s wort significantly reduces the bioavailability of verapamil. Other calcium channel blockers 
  would be expected to interact similarly
HDI category: A potentially hazardous combination
Glucosamine Metformin In a controlled study, glucosamine supplements with chondroitin had no effect on glycaemic control in 
  patients taking oral antidiabetic drugs, but increases in blood glucose concentrations have occurred in  
  patients with treated and untreated diabetes
Omega 3 fish oil Bisoprolol [2] The hypotensive effect of propranolol might be enhanced by fish oils
Ginkgo Rabeprazole Ginkgo modestly reduces omeprazole levels. Most other proton pump inhibitors are likely to be  
  similarly affected
HDI category: Doubt about outcome of concurrent usec
Omega 3 fish oil Aspirin [2] The concurrent use of aspirin and fish oils caused at least additive effects on bleeding time in healthy 
  subjects, but clinical studies in patients taking aspirin alone and with clopidogrel have found no evidence 
  of an increase in incidence of bleeding episodes
Cod liver oil Aspirin [2] The concurrent use of aspirin and fish oils caused at least additive effects on bleeding time in healthy 
  subjects, but clinical studies in patients taking aspirin alone and with clopidogrel have found no evidence 
  of an increase in incidence of bleeding episodes
Cod liver oil Bisoprolol The hypotensive effect of propranolol might be enhanced by fish oils 
 Propranolol 
Flaxseed Rivaroxaban Limited evidence suggests that flaxseed oil may have some antiplatelet effects, which could be additive 
  with those of conventional antiplatelet drugs, and increase the risk of bleeding with anticoagulants
Green tea Lisinopril Both black and green tea might cause a modest increase in blood pressure, which might be detrimental  
  to the treatment of hypertension. Green tea reduced the effects of nadolol on blood pressure in  
  healthy subjects
Senna pods Indapamide Theoretically, patients taking potassium-depleting diuretics could experience excessive potassium loss if  
  they also regularly use, or abuse, anthraquinone-containing substances such as senna
Glucosamine Co-codamol Limited evidence suggests that glucosamine might reduce the efficacy of paracetamol (acetaminophen) 
 Paracetamol 
Glucosamine Furosemide Limited evidence from a large open study suggests that unnamed diuretics might slightly reduce the 
 Bendroflumethiazide [2] efficacy of glucosamine to some extent
Echinacea Midazolam   Echinacea does not appear to alter the AUC and clearance of oral midazolam, although the bioavailability 
  may be increased. Clearance of intravenous midazolam may be modestly increased in patients taking  
  Echinacea
Hawthorn Nifedipine  Limited evidence suggests that there may be additive blood pressure-lowering effects if hawthorn is  
  taken with conventional antihypertensives, but the effects are small
Visionace® (Vitabiotics)  Lansoprazole The desired effect of betacarotene supplementation may be reduced in those taking proton pump 
(lutein, carotenoids, myrtillus,   inhibitors 
flavonoid compounds) 
Evening primrose oil  Aspirin Evening primrose oil can inhibit platelet aggregation and increase bleeding time. It has therefore been  
  suggested that it may have additive effects with other antiplatelet drugs, but evidence of this is generally  
  lacking
aThe number of patients exposed to the particular combination of HMPs/dietary supplement and prescription drug. bPotential interaction reports from Stockley’s Herbal 
Medicines Interactions. cGuidance about possible adverse effects and/or some monitoring may be needed. AUC = area under the curve. HDI = herb–drug interaction. 
HMP = herbal medicinal product.
5  British Journal of General Practice, Online First 2018
and recorded medications.26,27,31,35,36 Some 
patients do not consider HMPs and dietary 
supplements as medicines. Even when 
questioned, they may not always remember 
to disclose them. This highlights the need 
for direct questioning and for healthcare 
practitioners to ask about use of those 
HMPs and supplements by name, which 
this research has shown to be most at risk 
of interactions.
All older adults in the study sample were 
using at least one prescription drug; the 
range of prescription drugs was similar to 
those reported by older adults in a previous 
US study.37 The number of prescription 
drugs taken ranged from 1 to 18, with 
35% of the sample taking ≥5 prescription 
medications. This is consistent with findings 
of a study among US adults38 and UK data.39 
The number of HMPs and supplements 
used by the study participants ranged from 
1 to 8, and unexpectedly almost half of the 
concurrent users were using ≥3 HMPs and 
supplements.
Certain demographic and clinical 
characteristics are associated with 
concurrent medicine use. Females,13,36 
older age groups,35 people with chronic 
conditions such as diabetes and high blood 
pressure,3,31 people with less than high 
school education,31,40 and people on low 
income40 are more likely to be concurrent 
users. The finding that 43.4% of females 
were concurrent users compared with 
22.5% of males confirms previous findings 
that women tend to use more herbal and 
dietary supplements.13,14,36 The increased 
odds for a co-user to be female (34% 
versus 18%, P = 0.001) has been previously 
reported.34 This is likely to be for many 
reasons: women generally tend to live 
longer than men,41,42 they are the main 
carers for children and older people,43 tend 
to buy medicines and remedies for the 
home, and also tend to use more weight-
loss products than men.44 
Age was not significantly associated with 
concurrent use in this study, and in two other 
similar studies.31,32 However, concurrent 
use was highest among the participants 
in the age group 65–74 years (34.9%) but 
declined among those ≥85 years. Arcury 
et al45 reported significant association 
between age and use of herbal remedies 
but observed a similar trend of decreased 
use among those aged ≥75 years.
Implications for practice
This research has highlighted potential risk 
of interactions with certain combinations 
of prescription drugs, HMPs, and dietary 
supplements. Therefore, healthcare 
professionals should routinely ask 
questions regarding use of other 
medications that are not prescribed. The 
problem with recall and what patients think 
are HMPs or supplements or not needs 
to be addressed. There are stages in the 
process of prescribing and dispensing that 
could also be optimised, such as, printing 
a warning on prescriptions or looking 
at counselling given by pharmacists on 
dispensing. Targeted questioning about use 
of any alternative medicine or supplements 
could initiate conversations about wider 
HMP use and possible interactions. Liaising 
with community pharmacists could also 
raise awareness of a potential problem, 
particularly for older people on warfarin 
and statins.
Funding
No sources of funding were used to assist in 
the conduct of this study or the preparation 
of this article.
Ethical approval
Ethics review and support were obtained 
from the London — Hampstead Research 
Ethics Committee (15/LO/1870). 
Provenance
Freely submitted; externally peer reviewed.
Competing interests
The authors have declared no competing 
interests.
Open access
This article is Open Access: CC BY 4.0 
licence (http://creativecommons.org/ 
licences/by-nc/4.0/).
Acknowledgements
The authors thank all the patients and 
general practices that participated in this 
study. The authors also thank the Patient 
in Research Group (PIRg) of the Centre for 
Research in Public Health and Community 
Care (CRIPACC), for reviewing and 
suggesting changes to the study protocol, 
questionnaire, and participant information 
sheets.
Discuss this article
Contribute and read comments about this 
article: bjgp.org/letters
British Journal of General Practice, Online First 2018  6
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