Who Has Been Studied in PTSD Clinical Trials?

The PTSD-Repository includes 318 clinical trials. What we learn from randomized controlled trials (RCTs) helps us to decide what the best treatments are. We also learn which treatments need more research to know if they are helping people recover from PTSD.
Each RCT has a sample of diverse people. So, who are the participants in these clinical trials? Understanding who participates in research tells us how "generalizable" the results are. That is, to what extent the findings from given studies (or a sample) apply to the rest of the population or even to ourselves if we are considering treatment.
To learn more about the development of the PTSD-Repository, see About the PTSD-Repository.

How Old Are Clinical Trial Participants?

The PTSD-Repository includes clinical trials of adults, so in each study, participants were 18 years of age or older. Across all studies that report mean age data (N=297), the average age of participants is 40 years (range of 19-71 for all studies).
The mean age of participants is relatively consistent across treatment type (referred to as study class in the PTSD-Repository). Mean age is 39 for psychotherapy trials (N=148), 39 for pharmacotherapy trials (N=78) and 41 for RCTs that combined psychotherapy and pharmacotherapy (N=23). RCTs that included complementary and integrative health (CIH) modalities had somewhat higher mean ages: 47 for CIH only studies (N=17) and 48 for combined psychotherapy and CIH studies (N=7).  Nonpharmacologic biologic studies (N=8) also include somewhat older participants on average, with a mean age of 48. Alternatively, nonpharmacologic cognitive studies (N=4) include younger participants, with a mean age of 33. Collaborative care RCTs (N=4) and studies with another combination of treatments ("other mixed"; N=8) report average sample age of 40. 


Clinical Trials: Age

This histogram shows how mean age varies across the 297 studies that include information to determine the average age of participants. 

Are Clinical Trials Racially and Ethnically Diverse?

Understanding race and ethnicity differences in PTSD treatment initiation, completion and efficacy is a growing focus in the trauma literature. Federal funding sources require standard representation and reporting of race and ethnicity in clinical trials, although studies may be funded by non-government sources, or not report race and ethnicity data in publications. In addition, study designs may oversample—or seek to recruit--specific race and ethnicity groups to allow for participant pools large enough to conduct statistical comparisons between groups. Although more work in this area is needed, we are learning about race and ethnicity differences that may lead to approaches that benefit treatment engagement.  
Given the importance of this topic, it is disappointing that only 56% of studies included in the PTSD-Repository report race or ethnicity of participants. More specifically, 55% of studies report race information, and only 27% of studies report ethnicity of participants. Just under half of RCTs that ask about race also assess ethnicity, and for only 2 studies, ethnicity is reported without race information. Interact with the chart below to learn about race and ethnicity reporting by study class (treatment type); choose a bar to see how that reporting category varies by treatment.   

Clinical Trials: Race & Ethnicity Reporting

There are 16 RCTs with a sample that is at least 50% Black (1 of which was 95% Black). Nine RCTs report a sample that is at least 50% “other race” which is generally defined in the studies as “non-White,” with one study noting multiracial identity among 20% of participants. Two studies are Asian samples, 1 is a study of cognitive behavioral therapy with Cambodian refugees, the other an RCT of sertraline for PTSD in China. None of the studies were at least 50% American Indian / Alaskan Native.
Regarding ethnicity, 5 RCTs are at least 50% Latinx, including 1 pilot study that compared culturally adapted cognitive behavioral therapy to applied muscle relaxation among Latina women.

Race & Ethnicity Reporting Over Time

Consistent reporting of race and ethnicity is still in need of attention. Prior to 1996, few studies reported race of participants and ethnicity was less commonly included until later. This does not suggest that non-White participants were excluded or not part of research studies; however, publications did not highlight this information.

Are Clinical Trials Open to Men and Women?

Some of the earliest clinical trials of PTSD psychotherapies focused on women who experienced rape. As trials turned to Veteran samples, more men were included in research. Although women are slightly less likely to experience trauma in their lives, the types of traumatic events that lead to PTSD (e.g., sexual assault, child assault) are more common among women and prevalence of PTSD is slightly higher for women. As with race and ethnicity, gender may affect treatment initiation and engagement. And with the inclusion of men and women in clinical trials, the field is beginning to learn how gender may impact treatment efficacy. 

Clinical Trials: Gender

In the PTSD-Repository, only a small portion, 6% of studies, do not include gender information for participants. 15% of trials are limited to men, and 12% of studies focus on samples that are exclusively women. The large majority (67%) of trials include both men and women. 
You can "drill down" in the pie chart by selecting a slice, which shows you the overlay of study class for that given classification. For example, among the 12% of RCTs that are only women, most (74%) are psychotherapy trials. Among the 15% of studies that are limited to men, there is more parity between psychotherapy (38%) and pharmacotherapy (26%) studies. 

Where in the World Are Clinical Trials Being Done?

Almost two-thirds (62%) of studies in the PTSD-Repository were completed in the United States. 17% were based in European countries and 11% of RCTs are from the Middle East. Canada (6 RCTs), Asia (5), South America (3), and Africa (3) are also represented. An additional 6 studies are international samples. An important note here is that the PTSD-Repository is limited to studies published in English. Therefore, what is described here is only a subset of all the RCTs, although many trials from other countries are published in English. Interact with the map below to view the number of studies specific to each country. 

Clinical Trials: Map


How Important Are Military Studies?

The risk for trauma exposure in the military is significant and the willingness of Veterans and active duty to participate in research advanced the field's knowledge of how treatments work in this population. As with early studies of psychotherapy for women who experienced rape, Veterans and Active Duty members who participate in RCTs not only give themselves an opportunity to receive treatment to help them recover, but extend that benefit to anyone who may ultimately need PTSD treatment.

Clinical Trials: Military & Community Samples

The majority of RCTs (57%) are community-based, and although Veterans and Service members may be included in those samples, military status was not a focus of recruitment. 9% of RCTs are "mixed" samples, meaning both military personnel and civilians are included. The remaining studies are limited to military personnel, with 29% of RCTs specific to Veterans and 3% limited to Active Duty.  
Interestingly, looking at Veteran-specific RCTs by study type, complementary and integrative health (CIH) trials are more common than in community samples (see below). Over half (56%) of CIH studies are Veteran-only samples. This may reflect recent efforts by VA to better understand the efficacy of CIH for PTSD. Veteran samples also make up half of the Collaborative Care studies, as trials based on interventions that integrate medical and mental health care are much more possible within a comprehensive health care system like VA.

Clinical Trials: Gender & Military

Interact with the pie chart to see how studies that have all male (15%) or all female (12%) samples vary by military status. Not surprisingly, the majority of RCTs limited to men (89%) are Veteran-specific; RCTs with all female participants are primarily (85%) community samples. This may change over time as women are a growing proportion of Veterans.

What Do We Know About Trauma Types?

Determining trauma type classifications for RCTs in the PTSD-Repository is complicated because assessment of trauma history varies greatly across studies. In some cases, trauma assessment is limited to whether participants have experienced a specific trauma type of interest for a study, for example sexual assault or military trauma. In other cases, assessment includes obtaining information on all the types of traumas study participants experienced. Some studies look even further into the number of times a trauma type is experienced as well. 
Knowing information about the type(s) or number of traumas experienced by participants in treatment trials is valuable for two reasons. First, the type of trauma is important because we want to know if specific traumatic events are associated with different treatment outcomes.
Second, knowing the number of traumas experienced (or the number of different types of traumas experienced) provides information about the PTSD severity of the sample being studied. Experiencing multiple traumas is associated with increased PTSD symptom severity. Amount of traumatic exposure can affect whether or not findings are generalizable (applicable) in terms of treatment efficacy.
In the PTSD-Repository, most studies (88%) collect trauma history information. Assessing for trauma is part of the PTSD diagnostic practice; however, research participants may be included based upon diagnostic history, through self-report or chart review. In most studies with trauma history information, participants report a variety of traumatic experiences; and, the average number of trauma types reported by participants in RCTs that collect such information is about 9 (N= 14 RCTs with a total of 1547 participants). Within the 25 studies that count number of traumatic events--some reporting multiple types of events, others reporting multiple events of the same type--the mean is 7 traumas (N=25 RCTs with a total of 2043 participants). See the scatter plots below for more details.
The chart below shows RCTs that focused on specific trauma types by study class. Noticeably, the focus on military (Active Duty and Veteran) samples who have been exposed to combat-related trauma offers the most variety of treatment RCTs. 

Are Clinical Trial Participants Naive (New) to Treatment?

As we strive to learn about treatment engagement, preference and efficacy, one potential factor for investigation is to consider whether participants are new to PTSD treatment. This is important because, for example, a study participant who did not benefit from previous treatments will be less likely to meet treatment goals than a participant who is in treatment for the first time.
Overall, 79% of studies do not report whether or not participants have a history of PTSD treatment. Three psychotherapy RCTs only include participants that are new to PTSD treatment. This can be an important factor to consider in relation to both treatment engagement (e.g., willingness to commit time to therapy appointments) and treatment outcomes. Importantly, this is representative of only 10% of psychotherapy RCTs that report treatment history (N=31). In 32% of these studies, all of the participants reported prior PTSD treatment experiences. 
Among the 83 pharmacotherapy trials included in the PTSD-Repository, 83% do not ask about PTSD treatment history and of those that did, all include at least some participants with prior PTSD treatment. Almost two-thirds of pharmacotherapy RCTs report that all participants in the given study have taken medications (e.g., antidepressants) in the past. 

How Common Are Comorbidities in Clinical Trials?

It is common for people who have PTSD report having co-occurring conditions such as depression, substance use disorder (SUD) or a history of traumatic brain injury (TBI). These comorbidities may be important considerations for treatment planning and can affect treatment dropout and outcomes. For example, following the wars in Iraq and Afghanistan, there was a lot of attention paid to TBI. It was called the "signature wound" of these conflicts (U.S. Department of Defense, 2014). However, most studies do not assess whether participants have a history of TBI (90%). And, of those that do, participants with severe TBI history are excluded from the trial. Combined psychotherapy & pharmacotherapy trials are more likely to assess for a history TBI (22% of them, compared to the 10% overall). Even among Veteran studies, only 12% report on TBI history.
In particular, SUD is an important co-occurring condition both in regard to study inclusion—as some RCTs exclude participants who have a severe SUD—and for the evaluation of treatments specific to patients who have both PTSD and SUD. Moving forward, the PTSD-Repository will offer more detailed variables about SUD with updates available in 2021

Clinical Trials: PTSD & Depression

Over three-quarters of people with PTSD also have another disorder (Kessler, 1995).  Depression is common in people with PTSD, with the National Comorbidity Survey reporting major depression co-occurring for 48% of men and 12% of women with PTSD (Kessler, 1995). Most (61%) of the RCTs included in the PTSD-Repository do not include assessment for depression. The RCTs that assess for depression and report including participants with no depression comorbidity are more commonly pharmacotherapy trials, which suggests a focus on isolating drug benefits for PTSD specifically. 

Wrapping Up

The studies included in the PTSD-Repository provide rich information about clinical trials for PTSD. As researchers work to better understand treatment outcomes, a continued focus on diversity among study participants will also help identify for whom particular treatments may work best. This data story shows the need for more attention to reporting of demographic information for participants, trauma and treatment histories, and comorbidity assessment.

References

Kessler, R. C., Sonnega, A., Bromet, E., Hughes, M., & Nelson, C. B. (1995). Posttraumatic stress disorder in the National Comorbidity Survey. Archives of General Psychiatry, 52(12), 1048-1060. https://doi.org/10.1001/archpsyc.1995.03950240066012
U. S. Department of Defense. (2014). Traumatic Brain Injury: Department of Defense Special Report. Retrieved from: http://www.defense.gov/home/features/2012/0312_tbi/