UMIN-ICDS Clinical Trial

Public title

An Empirical Study of Nudge-Based Interventions to Enhance Trust in Generic Drugs and Promote Their Use

Acronym

Nudges to Promote Generic Drug Use

Scientific Title

An Empirical Study of Nudge-Based Interventions to Enhance Trust in Generic Drugs and Promote Their Use

Scientific Title:Acronym

Nudges to Promote Generic Drug Use

Region

Japan

Condition

No specific condition

Classification by specialty

Not applicable

Adult

Classification by malignancy

Others

Genomic information

NO

Narrative objectives1

This study aimed to assess whether loss- and gain-framed nudges highlighting the price difference under Japan's cost-sharing policy for long-listed drugs increased intention to use generic drugs immediately after the intervention and self-reported generic drug uptake two months later, compared with a neutral control message. The study focused on adults who reported not using generic drugs or being unsure whether they used them and who had low trust in their safety and effectiveness. We also examined whether these effects differed by sex.

Basic objectives2

Efficacy

Basic objectives -Others

Trial characteristics_1

Confirmatory

Trial characteristics_2

Explanatory

Developmental phase

Not applicable

Primary outcomes

Intention to use generic drugs immediately after exposure to the assigned message at Wave 1 (15-19 May 2025). Agreement with the statement "I would like to use generic drugs" was assessed on a five-point Likert scale ranging from 1 ("strongly disagree") to 5 ("strongly agree"). Responses were dichotomised as intention to use (scores 4-5) or no intention to use (scores 1-3).

Key secondary outcomes

Self-reported generic drug uptake approximately two months after exposure to the assigned message at Wave 2 (15-19 July 2025). Participants who reported visiting a healthcare provider during the follow-up period were asked whether they were currently using generic drugs.

Study type

Interventional

Basic design

Parallel

Randomization

Randomized

Randomization unit

Individual

Blinding

Single blind -participants are blinded

Control

Active

Stratification

NO

Dynamic allocation

NO

Institution consideration

Institution is not considered as adjustment factor.

Blocking

NO

Concealment

Central registration

No. of arms

3

Purpose of intervention

Educational,Counseling,Training

Type of intervention

Behavior,custom

Interventions/Control_1

At Wave 1 (15-19 May 2025), after receiving the common standardized policy explanation, participants viewed the following loss-framed nudge message once online: "If you choose a brand-name drug instead of a generic drug, you will be required to pay a special fee equal to one-quarter of the price difference between the two drugs. As a result, your out-of-pocket medication costs may increase by approximately 30-50%." No additional intervention was provided at Wave 2.

Interventions/Control_2

At Wave 1 (15-19 May 2025), after receiving the common standardized policy explanation, participants viewed the following gain-framed nudge message once online: "If you choose a generic drug instead of a brand-name drug, the special fee equal to one-quarter of the price difference between the two drugs will be waived. As a result, your out-of-pocket medication costs may decrease by approximately 20-30%." No additional intervention was provided at Wave 2.

Interventions/Control_3

At Wave 1 (15-19 May 2025), after receiving the common standardized policy explanation, participants viewed the following neutral control message once online: "If you choose a brand-name drug instead of a generic drug, you will be required to pay a special fee equal to one-quarter of the price difference between the two drugs." No additional intervention was provided at Wave 2.

Interventions/Control_4

Interventions/Control_5

Interventions/Control_6

Interventions/Control_7

Interventions/Control_8

Interventions/Control_9

Interventions/Control_10

Age-lower limit

18

years-old

<=

Age-upper limit

Not applicable

Gender

Male and Female

Key inclusion criteria

Participants were eligible if they met all of the following criteria: (1) were aged 18 years or older; (2) were able to choose a generic drug; (3) reported that they were not currently using generic drugs or were unsure whether they were using them; (4) had low trust in generic drugs, defined as a score of 3 or lower for both the statements "Generic drugs are safe" and "Generic drugs are effective" on five-point Likert scales ranging from 1 ("strongly disagree") to 5 ("strongly agree"); and (5) provided electronic informed consent.

Key exclusion criteria

Participants were excluded if they met any of the following criteria: (1) were younger than 18 years; (2) were unable to choose a generic drug; (3) reported that they were currently using generic drugs; (4) scored 4 or higher on either the perceived safety or perceived effectiveness item and therefore did not meet the definition of low trust in generic drugs; or (5) did not provide electronic informed consent.

Target sample size

2500

Name of lead principal investigator

1st name	Chenyue
Middle name
Last name	Huang

Organization

Institute for Health Economics and Policy

Division name

Research Department

Zip code

1050001

Address

3F, Tokyu Toranomon Building, 1-21-19 Toranomon, Minato-ku, Tokyo, Japan

TEL

0335068529

Email

shinetsu.ko@ihep.jp

Name of contact person

1st name	Chenyue
Middle name
Last name	Huang

Organization

Institute for Health Economics and Policy

Division name

Research Department

Zip code

1050001

Address

3F, Tokyu Toranomon Building, 1-21-19 Toranomon, Minato-ku, Tokyo, Japan

TEL

0335068529

Homepage URL

Email

shinetsu.ko@ihep.jp

Institute

Institute for Health Economics and Policy

Institute

Department

Personal name

Huang Chenyue

Organization

Ministry of Education, Culture, Sports, Science and Technology

Organization

Division

Category of Funding Organization

Japanese Governmental office

Nationality of Funding Organization

Japan

Co-sponsor

Name of secondary funder(s)

Organization

Institute for Health Economics and Policy

Address

3F, Tokyu Toranomon Building, 1-21-19 Toranomon, Minato-ku, Tokyo, Japan

Tel

0335068529

Email

info@ihep.jp

Secondary IDs

YES

Study ID_1

R6-006

Org. issuing International ID_1

Institute for Health Economics and Policy

Study ID_2

Org. issuing International ID_2

IND to MHLW

Institutions

Date of disclosure of the study information

2026

Year

07

Month

24

Day

URL releasing protocol

The protocol is not publicly available.

Publication of results

Published

URL related to results and publications

The protocol is not publicly available.

Number of participants that the trial has enrolled

2500

Results

[Oral presentation] Huang C, Innami I. An empirical analysis of the effects of nudges on intention to use and uptake of generic drugs. The 19th Annual Meeting of the Association of Behavioral Economics and Finance; December 13, 2025.

Results date posted

2026

Year

07

Month

24

Day

Results Delayed

Results Delay Reason

Date of the first journal publication of results

Baseline Characteristics

The Wave 1 analysis included 2,500 participants: 834 in the loss-framed group, 833 in the gain-framed group, and 833 in the control group. Values are presented below in the order loss-framed/gain-framed/control.
Mean age (SD) was 53.0 (13.0)/53.7 (13.1)/53.7 (12.9) years. The numbers of male participants were 505 (60.6%)/523 (62.8%)/510 (61.2%), and the numbers of female participants were 329 (39.4%)/310 (37.2%)/323 (38.8%).
Educational attainment was below university degree for 508 (61.3%)/498 (60.1%)/473 (57.1%) participants and university degree or higher for 321 (38.7%)/330 (39.9%)/355 (42.9%) participants. Educational attainment was missing for five participants in each group; percentages were calculated among participants with available data.
Annual household income was less than JPY 4 million for 287 (34.4%)/311 (37.3%)/283 (34.0%) participants, JPY 4 million to less than JPY 8 million for 211 (25.3%)/237 (28.5%)/233 (28.0%), JPY 8 million or more for 142 (17.0%)/123 (14.8%)/138 (16.6%), and unknown for 194 (23.3%)/162 (19.4%)/179 (21.5%). The unknown category included responses of "don't know" and "prefer not to answer."
Mean baseline intention to use generic drugs (SD), measured on a five-point scale, was 2.9 (0.8)/2.9 (0.7)/2.9 (0.8). Baseline characteristics were broadly similar across the three groups.

Participant flow

At Wave 1 (15-19 May 2025), 27,744 online panel members were assessed for eligibility. Of these, 25,244 (91.0%) were excluded because they met one or more of the following criteria: aged younger than 18 years, no option to choose a generic drug, currently using generic drugs, or high trust in generic drugs.
The remaining 2,500 eligible participants were randomised in a 1:1:1 ratio to the loss-framed group (n = 834), gain-framed group (n = 833), or control group (n = 833). All 2,500 randomised participants were included in the Wave 1 intention analysis, with no post-randomisation exclusions.
At Wave 2 (15-19 July 2025), the follow-up survey was closed when the prespecified target of 1,000 completed responses was reached. Respondents comprised 334 participants in the loss-framed group, 333 in the gain-framed group, and 333 in the control group. The remaining 1,500 participants were not included among the completed Wave 2 respondents.
Of the 1,000 Wave 2 respondents, 337 who reported visiting a healthcare provider during the follow-up period were included in the generic drug uptake analysis: 109 in the loss-framed group, 113 in the gain-framed group, and 115 in the control group. The remaining 663 respondents who reported no healthcare visit were excluded from the uptake analysis: 225 in the loss-framed group, 220 in the gain-framed group, and 218 in the control group.

Adverse events

The intervention consisted of a one-time online presentation of an informational message. Adverse events were not prespecified as an outcome or systematically collected. No adverse events were reported in the published article.

Outcome measures

The primary outcome was intention to use generic drugs immediately after exposure to the assigned message at Wave 1. Participants rated their agreement with the statement "I would like to use generic drugs" on a five-point Likert scale ranging from 1 ("strongly disagree") to 5 ("strongly agree"). Responses were dichotomised as intention to use (scores of 4 or 5) or no intention to use (scores of 1-3). Baseline intention was assessed before message exposure using the same item and scale.
The secondary outcome was self-reported generic drug uptake at Wave 2, approximately two months after message exposure. Participants who reported visiting a healthcare provider during the follow-up period were asked whether they were currently using generic drugs. Uptake was assessed on the basis of their responses.

Plan to share IPD

IPD sharing Plan description

Recruitment status

Completed

Date of protocol fixation

2025

Year

03

Month

20

Day

Date of IRB

2025

Year

04

Month

14

Day

Anticipated trial start date

2025

Year

05

Month

15

Day

Last follow-up date

2025

Year

07

Month

19

Day

Date of closure to data entry

2025

Year

07

Month

19

Day

Date trial data considered complete

2025

Year

08

Month

30

Day

Date analysis concluded

Other related information

Registered date

2026

Year

07

Month

24

Day

Last modified on

2026

Year

07

Month

24

Day

Link to view the page

Value
https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000071327