In my short experience as a research coordinator in National University of Singapore Obstetrics & Gynecology Department, handling multiple research projects from different principal investigators and the demand to provide biological samples whenever possible, consenting a patient to multiple studies at once or sequentially during the pregnancy has been a strategy that we have adopted. The investigators that I was working with were aware of this practice; however, ethical issue was raised when a clinical research team called our attention not to recruit their patients because the investigational product that they were introducing to patients may affect the quality of biological specimen that we are collecting. Another principal investigator from another research team had instructed us not to consent their patients because it is unethical to consent one patient to several studies. Looking into the literature for this research question, I have encountered the term co-enrolment which is also being practiced in other developed countries such as US, Canada, UK, Australia and New Zealand (Cafferty et al., 2017; Cook et al., 2013; Harron et al., 2012; Myles et al., (2014). According to Bucukoglu (2018), Cafferty et al. (2017), Cinnella (2015), co-enrolment is defined as recruitment of one patient in two or more research at the same time or in overlapping studies at different period. At present there is no clear international guidelines about co-enrolment (Cinnella, 2015), although the US FDA (2014) has made draft recommendations against enrolment of patients in more than one clinical trial due to safety reasons and the risks that patients may not truly understand the consent forms and responsibilities demanded of them. There is an insufficient information about co-enrolment (Cafferty et al., 2017; Cinnella, 2015) and there is a possibility that the local ethics board committee are not aware of its prevalence. Meanwhile, industry-sponsored trials have been clear and strict with their guidelines against participation of patients in several clinical trials (Myles et al., 2014; Cinnella, 2015) that has not passed the wash out period as specified in their protocol inclusion and exclusion criteria or clinical trial agreement. This policy is justifiable because of concerns of drug to drug interaction, scientific validity, and adverse events liability (Krige et al., 2013; Myles et al., 2014). On the other hand, certain areas such as HIV AIDS and critical care studies promote co-enrolment (Myles et al., 2014). The federally funded clinical trial organization called The Terry Beirn Community Programs for Clinical Research on Acquired Immunodeficiency Syndrome (CPCRA) in the US has developed guidelines in co-enrolment (Myles, Williamson, Oakley, & Forbes, 2014). The CPCRA have strategies in informed consent process for patients who are eligible to participate in several clinical trials during the study period, data sharing in all studies, single clinic visits based on the first study the patient has enrolled in, and using the modified factorial study design (Randolph, 2009). This community setting research has long term follow ups of patients and during the course of treatment, their status may change which may make patients eligible for other studies. Therefore, this group aims to understand the process and response of patients in every treatment regimen and the interaction between drugs to design a better protocol for HIV patients (ASPE, 2000). In this case, co-enrolment in different trials may enhance HIV AIDS treatment regimen design which is still relatively new and there’s an existing demand to find a cure.The Australian and New Zealand Intensive Care Society (ANZICS) Clinical Trial Group also support simultaneous or sequential participation of patients in clinical trials (Krige, Pattison, Booth, & Walsh, 2013). According to Randolph (2009), there are different interventions done to patients in intensive care that are not proven effective and yet implemented to save the lives of patients. Moreover, the growing number of clinical trials in intensive care with limited number of patients could lead to recruitment competition among the researchers (Krige et al., 2013). Co-enrolment could be addressing these two issues by studying the interaction and effectivity of procedures or treatments and reducing the pressure to be the first to recruit the patients. On the other hand, the patients in critical care units are usually incapable of giving their informed consent and the decision must be made by a legally acceptable representative. Despite the acceptability of co-enrolment in developed countries, a tri-nation survey involving Canada, New Zealand, and Australia revealed that only 11% of local ethics committee and 35% of critical care units have policy in co-enrolment (Cook et al., 2013). Some researchers report that obtaining ethics approval for studies involving co-enrolment is a hindrance (Cafferty et al., 2017) because most IRB consider this practice as unethical and burden to patient due to safety concerns, overwhelming patients with informed consent, scientific integrity, and causing additional stress to patients or relatives who are already in a challenging situation (Cook et al., 2013). Therefore, the approval for co-enrolment differs from one institution to another. The ethical concerns of co-enrolment is also shared by some investigators who detract from this practice as a safe option due to lack of international guidelines (Cafferty et al., 2017) and apprehension that they may overburden and cause harm to patients. On the other hand, half of clinicians and study coordinators (52%) in Australia, New Zealand, and Canada have reported recruitment of one patient to more than one study in ICU settings and the experience of researchers played a huge role in their tendency to co-enrol. As far as I know, there is no published literature disputing co-enrolment practices. The absence of straightforward international guidelines in co-enrolment of investigator-initiated trials, pragmatic trials, and non-interventional research combined with multiple trials in one site place the investigators in a dilemma to co-enrol or prioritize recruitment in one study. The former may entail withholding information to patients who are eligible to participate in more than one study. According to Myles, Williamson, Oakley, & Forbes (2014), investigators should inform the patients of studies that they are eligible to participate in. This is supported by Randolph (2009) as the author stated that patients may want to know what studies are available for them and make decisions. Furthermore, it is considered paternalistic to prevent capable and independent individuals to decide what is good for them (Myles, Williamson, Oakley, & Forbes, 2014). Literature has supported co-enrolment and negated the issues of burden, safety and scientific integrity. Furthermore, authors such as Myles et al. (2014) and Cafferty et al. (2017) believe that the autonomy of patients should be observed in recruitment of patients. In Belmont Report, autonomy is described as non-interference of a capable person’s opinion except when it can result to harm to others, and providing all the facts for the person to make judgment for himself/herself. Hence, the decision of the IRB and some investigators to fully restrict co-enrolment despite unproven evidence of negative consequences can be viewed as limiting patients opportunity (Cafferty et al., 2017), unnecessary, and a practice of paternalism (Myles et al., 2014; Krige et al., 2013). In a survey done in Australia, 98% of 50 families with admitted infants in Neonatal Intensive Care Unit reported that they would prefer to make decisions in research participation for their babies than done by their healthcare providers and 74% of these parents were willing to include their offspring in more than one study (Cafferty et al., 2017). Independent decision-making is highly valued by these parents and their willingness to co-enrol their babies maybe compelled by the reason that patients enrolled in research receive a more focused care. In some circumstances, the same clinicians are the investigators of these studies (Ward, 2010) whom the parents may have developed trust and believed that their doctors know the best treatment and care of their babies. Burden in co-enrolment of patients was proven to be untrue in another survey done in UK. Among the breast cancer patients, 64% of 50 respondents dismiss the idea that participation in two or more trials is a burden; 86% believed that the demand asked of them in co-enrolment would not be over of what is explained; and 74% would enroll in more than one study as long as they are given enough information (Burnet et al., 2004). Harron et al. (2012) also reported in his article about co-enrolment of patients in 2 pragmatic clinical trials in Pediatric Intensive Care Unit that information overload among parents was not listed as a reason for declining research participation. However, there were reports from nurses that some parents are burdened by making decisions in a stressful situation. Co-enrolment in HIV AIDS patients in the community and critical care settings may empower patients with autonomy and provided with the opportunity to experience different treatment that maybe beneficial for them or future patients; however, there should be careful consideration of these patients in ensuring their safety and convenience. Even if these patients are competent adults who can make sound decision-making, the mere fact that they are in need of care and dealing tremendous stress due to their health status, ensuring a true informed consent and assessing the burdens of patients should be the priority. In addition, the disadvantaged population such as the economically and educationally challenged should be afforded with extra protection.Myles et al., (2014) and Krige et al. (2013) argue that protection in competent individuals who understand the risk and benefits of their decisions, and will not result in negative repercussions is unjustifiable. In medical treatment, all options are presented to patients pertaining to their illness; thus, they should be given all the options too in research (Krige et al., 2013). This is giving an equal opportunity to potential patients to participate in research that may be important for them, and patients should not be denied of this opportunity (Cafferty et al., 2017). Equal opportunity for eligible patients to participate in trials is fair selection of subjects under justice. Furthermore, there are patients who find fulfillment in research participation even if there was minimal benefit on them (Burnet et al., 2004).Reducing the burden of patients in research participation and providing equal opportunity in enrolment to research that patients’ value should have a middle ground in considering co-enrolment. As John Stuart Mill said “it is ethically justifiable to prevent a person from voluntarily selling himself into slavery” (Myles et al., 2014). Therefore, the decision to co-enroll patients should be weighed with the risk and benefits, ability to understand research participation, the vulnerability, and the situation the patient is currently facing. These are ethical issues that requires judgment of the investigator or research coordinator.There is also a huge concern about interaction between interventions in co-enrolment and affecting the scientific validity of each study. However, the ICU multi-center trials PROTECT: “Randomized, blinded clinical trial comparing unfractionated heparin to dalteparin for thromboprophylaxis” (Cook et al., 2013) and OSCILLATE “randomized clinical trial comparing high- frequency oscillation with conventional ventilation in patients with acute respiratory distress syndrome” (Cinnella, 2015) showed that the percentage of adverse events did not affect the overall results even if co-enrolled patients were excluded from analysis (Krige et al., 2013). Although Krige et al. (2013) also stated that the when the co-enrolment rate is too high, over 50%, this will affect the design and power of the studies. Therefore, there should be a maximum percentage of co-enrolment in each trial.Scientific integrity is a foundation in conducting research because the study outcome becomes the basis of medical treatment in patients. Ensuring reliability and validity of research is crucial in each study regardless if co-enrolment is practiced or not. Although in co-enrolment, extra measures should be taken to ensure that adverse events of patients are associated to the correct study. This will require an intensive observation and understanding the effects of each intervention. Therefore, the timing of interventions and effects should also be documented and evaluated. In addition, there is a need for more studies and considerations to design and ensure scientific validity of co-enrolment in clinical trials.With the issues surrounding co-enrolment, authors have listed the benefits of co-enrolment such as efficiency in recruitment (Cafferty et al., 2017; Krige et al., 2013; Randolph, 2009), rich research data (Randolph, 2009), solution to numerous research with limited patients, reduce the pressure in recruitment competition and conflicts (Krige et al., 2013), and enrolment to several studies could be beneficial to patients (Harron et al., 2012). According to Harron et al., (2012), achieving the target number of patients in a short period of time could lead to faster delivery of care to patients. Moreover, the interaction between interventions could help provide more information the treatment of patients (Cafferty et al., 2017). Lastly, sharing of patients in research may reduce possible conflicts arising from recruitment competition, and different interventions to one patient may lead to new treatment (Krige et al., 2013). The benefits listed by the authors wrap co-enrolment into a promising idea. However, every angle should be assessed and feasibility in each situation should be studied. There must be open and agreeable plans among the investigators (Harron et al., 2012) to ensure the safety and reduction of burden to patients. The concerns of safety, scientific validity, exploitation of patients, and burdening patients cannot be totally ignored especially in interventional trials and when the combination of interventions have been insufficiently studied. Continuous monitoring of patients to assess the burden and the option to withdraw anytime should be emphasized (Burnet et al., 2004). The consent process should be clear, voluntary (Cafferty et al., 2017), and free from undue influence or coercion. The timing of consenting patients (ANZICS CTG, 2015; Cafferty et al., 2017), assessment of understanding of patients, and judgment if patient is capable physically, emotionally, and mentally of participating in multiple studies should all be considered.Co-enrolment is acceptable and justifiable when the risk and for patients is not high and beneficial to patients and the society e.g. tissue collection with therapeutic or diagnostic procedure, blood collection, questionnaire, or observational trials. The risk and benefits ratio, non-exploitation of patients particularly the special populations, study validity, and respecting the autonomy and justice for patients should be balanced. There may be a need to enroll patients in multiple trials in the field of critical care and HIV AIDS, but this should not be practiced in research where there is sufficient pool of potential subjects. Safety and rights of patients should the priority before advancement in science.