Paying Participants to Take Part in Addiction Research: Ethical Considerations

Mary-Tara Roth, RN, MSN, MPH

Director, Clinical Research Resources Office, Clinical and Translational Science Institute, Boston University School of Medicine/Boston Medical Center, Boston, MA, USA

In many settings, research studies pay participants to help with recruitment, increase compliance with protocol requirements, and improve retention.1–3 The amount of payment depends on a range of factors. Is the study recruiting healthy individuals who do not have the condition under investigation, or individuals who may receive medical benefit from participation? What are the potential risks of participation? How much inconvenience is expected due to the number and length of study visits?

Reasons for Concern about Payments

Payment amounts are likely to depend on the particular aspects of the study population. For example, in addiction research, participants may be more likely to be poor, disenfranchised, and lacking a stable or sufficient income, and to have fewer social resources and support than the general population. Ethical concerns about paying individuals to take part in a study, especially one that may pose greater than minimal risk, are heightened for such populations.4 The main ethical concern, applicable to any study population, centers on whether participants take part in a study because of the payment, even when participation would not be in their best interest. In people with drug addiction, there are additional concerns about whether monetary or other payment might motivate more drug use or relapse, since cash or transferable goods on hand might be used to procure the drug of abuse.

These concerns relate to the possibility that informed consent would not be voluntary, and thus would not be valid. Human-subjects research regulations and ethical guidelines state that consent should be sought only when subjects have received sufficient information to consider the risks and benefits of participation, and that they decide to take part without the presence of coercion or undue influence.5 Thus, payment to research participants should be evaluated to ensure that it doesn’t increase potential for coercion or undue influence, which would threaten the validity of informed consent. The terms “coercion” and “undue influence” are sometimes used interchangeably; however, coercion is the threat of removing benefits to which someone is entitled to get him or her to participate. Undue influence is providing an attractive incentive to participate. Depending on the study and the study population, paying research participants could be seen as exerting undue influence, particularly when it leads to study participation that is not in an individual’s best interests.6 Coercion is easier to spot: “Take part in this study or you won’t be able to get care at the free clinic anymore.” Undue influence, however, may be more subtle and depend on other contextual factors: “Take part in this study and receive $100.” Researchers must determine at what point $100 could be considered undue influence.

Payment for taking part in research studies can encompass several types of transactions. While it often involves money, other forms of payment, such as course credit and in-kind payments, are used as well.3,7,8 Payment of some sort is not unusual9; however, some advocate for limitations, believing either that any inducement for participating in research adds to the difficulty subjects have in assessing risk, or that research should be an altruistic, socially responsible, humanitarian activity.10–12

Payment to Participants and the Belmont Principles

The 3 ethical principles of the Belmont Report13 provide the philosophical underpinnings of US human-subjects protection regulations. Assessing the ethics of payment to participants under these principles can help us understand the issues. Beneficence, the first principle, speaks to risks and benefits of a study: risks should be minimized, while benefits to the subject and society are maximized. A study may be judged as too risky for subjects based on the science, design, or level of monitoring. Since payment to research subjects should not be considered a “benefit”6,14 (i.e., a study is not more “beneficent” because it pays more), such payment must not be seen as offsetting the risks of the study. As such, the ethical concept of beneficence is usually not considered in assessing payment of participants.

The second principle, respect for persons, speaks to autonomy—the idea that an individual who is competent can make decisions on his or her own, and that the decision to take part in research is voluntary. The consent process supports this principle, ensuring that all the information about the purpose, risks and benefits of study participation have been related so potential subjects can make a fully informed decision. The question of whether payment affects a person’s ability to make a good decision comes up here, and we can quickly see the complexities involved. Will a $25 dollar payment at each study visit to account for 2 hours of time and transportation reimbursement sway an individual to participate at increased risk to himself? What if that amount is $40 per visit . . . or $80? How does the picture change if a potential participant is destitute and needs cash to buy food? In this case, could any payment amount have the potential for undue influence? On the other hand, is restricting payment because of this possibility rightfully protective of a vulnerable population subject to exploitation or instead paternalistic and disrespectful?

Last, the principle of justice speaks to equitable selection of research participants. Research that presents potential benefits should be accessible to all, and risks of research should not be endured only by those who happen to be more easily accessible to the researcher. A payment that is sufficient to attract people who have to take time off from work to participate may be extremely attractive to a person who is homeless, who may not fully assess the potential risks (undue influence). On the other hand, reducing the payment for the same study would likely limit the people who enroll to those who are not employed.

Does Payment for Research Participation Lead to Use of Drugs of Addiction?

Some experts consider addiction to hold too great a power over people, so that provision of cash, or even in-kind payment that could be transferred to cash, would be used to buy drugs.15,16 In response to such concerns, the market has provided possible solutions. One example is a credit card for people recovering from drug use ( This card limits the types of purchases that can be made, such as not allowing purchases at bars or liquor stores. The user also cannot use it to make ATM withdrawals or receive cash back when making purchases.

However, there growing empirical evidence that payment for research participation does not promote the purchase of drugs or lead to relapse. Dempsey et al.18 found that participants receiving $150–$300 either in cash or money order did not affect cocaine use the day of, or after, discharge. Festinger et al.19 randomly assigned participants to receive different amounts of cash or gift card payments. Neither the type of payment nor the amount (up to $70) had a significant effect on rates of new drug use. A subsequent study20 that tested higher payment amounts (up to $160) had similar findings. Vandrey et al.21 found that receipt of $100 checks did not increase subsequent rates of cocaine use compared with controls among participants in a contingency management program. Although more research in this area is needed, these studies call into question the commonly held assumption that a person with drug addiction who is given a sum of money will be driven by his addiction to use that money to buy drugs.

The IRB and Assessment of Payment

The amount that the study proposes to pay participants will be judged by an Institutional Review Board (IRB). Among other criteria, IRB members must determine whether risks to subjects are minimized and reasonable, that informed consent is properly obtained, and that selection of subjects is equitable.22 Although payment to subjects affects each of the aforementioned criteria, there are general guidelines (but no specific directives) in the regulations as to what amount is appropriate. One survey found that IRB members often struggle to determine at what point undue influence could occur in a study, and that their decisions are often based on members’ own perceptions rather than objective assessment.23

Understanding the ethical issues and being well-versed in the current empirical evidence surrounding compensation for participation in addiction research can help researchers justify to the IRB whether payment to subjects in a given study is appropriate, and if so, what amount, type, and disbursement schedule is ethically sound. A well-considered and ethically justified approach will always fare better in IRB review and promote ethical conduct of the study for participants.


The choice to take part in a research study can be complex and based on multiple factors including intrinsic personal beliefs and external influences. The possibility for undue influence exists in many research studies and is not always in the form of monetary payment (think, for example, of a new treatment for a severe disease with limited alternative options). For any population, when undue influence is a possibility, the consent process should underscore the potential risks and ensure that all subjects understand those risks and appreciate what they mean in relation to their own situations. People can make bad decisions about spending their money, and this possibility, of course, is not limited to people who use drugs. Although more research is needed (and there is a great opportunity for researchers in the addiction field to do this research, even in the context of ongoing studies), current evidence suggests that monetary payment does not make addiction-research participants more likely to buy and use drugs. Addiction researchers must navigate the potentially complex ethical gray area between allowing autonomous individuals to make their own decisions about study participation and providing protections to those who may have limited autonomy. 


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