Who Has Been Studied in PTSD Clinical Trials?
The PTSD-Repository includes 389 randomized controlled trials (RCTs) of treatments for PTSD. What we learn from RCTs helps us to determine which treatments are best. We also learn which treatments need more research to establish if they are helping people recover from PTSD.
PTSD can impact anyone. So, who are the participants in these clinical trials? Understanding who participates in research tells us how "generalizable" the results are. That is, we want to understand to what extent the findings from given studies (or sample) apply to the rest of the population or to ourselves if we are considering treatment.
How Old Are Clinical Trial Participants?
The PTSD-Repository includes clinical trials of adults, so in each study, participants were on average, 18 years of age or older. Across all studies that report mean age of the sample (n=366), participant groups are on average 42 years old (range of 19-71 across studies).
The mean age of participants is relatively consistent across treatment type (referred to as "study class" in the PTSD-Repository). Mean age is 40 for psychotherapy trials (n=180), 43 for pharmacotherapy trials (n=83) and 45 for RCTs that combined psychotherapy and pharmacotherapy (n=26). RCTs that included complementary and integrative health (CIH) modalities had somewhat higher mean ages: 47 for both CIH only studies (n=26) and combined psychotherapy and CIH studies (n=14). Nonpharmacologic biologic studies (n=12) also include somewhat older samples, with a mean age of 48. On the other hand, nonpharmacologic cognitive studies (n=6) include younger samples, with a mean age of 33. Collaborative care RCTs (n=5) and studies with another combination of treatments ("other mixed"; n=814) report average sample age of 41.
This histogram shows how mean age varies across the 367 studies that include information to determine the average age of participants. Use the filter to view mean age of the sample by primary type of treatment tested.
Are RCTs for PTSD Racially and Ethnically Diverse?
Understanding racial and ethnic disparities in PTSD treatment access, initiation, completion and efficacy is a growing focus in the scientific literature. Federal funding sources require standard representation and reporting of race and ethnicity in clinical trials. Studies funded by non-government sources may not report race and ethnicity data in publication findings. Some study designs may oversample—or seek to recruit--specific race and ethnicity groups to allow for sample sizes large enough to conduct statistical comparisons between groups. Although more work in this area is needed, research on how race and ethnicity relate to PTSD treatment helps us identify disparities and ensure that our treatments are effective for (and available to) everyone. To gain a deeper understanding of the research on racial and ethnic disparities in PTSD, please see the National Center for PTSD Research Quarterly (PDF) on this topic.
Unfortunately, only 57% of studies included in the PTSD-Repository report race information, and only 30% of studies report ethnicity of participants. Just over half of RCTs that report about race also report ethnicity (52%); and, for only 2 studies, ethnicity is reported without race information. Click on a bar within the chart below to learn about race and ethnicity reporting by study class.
Clinical Trials: Race & Ethnicity Reporting
There are 25 RCTs with a sample that is at least 50% Black (1 of which was 95% Black) and an additional 61 RCTs had samples that were between 25%-50% Black. None of the studies were at least 50% American Indian / Alaskan Native nor Asian American / Pacific Islander. There are 8 studies that are at least 10% Asian American. The PTSD-Repository also includes 2 studies focused on Asian samples; 1 is a study of cognitive behavioral therapy with Cambodian refugees in the United States, the other an RCT of sertraline for PTSD in China.
Regarding ethnicity, 5 RCTs are at least 50% Latina/o, 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 deliberately excluded or not part of research studies; however, recruitment efforts may not have reached participants of color or participants of color were included but publications did not highlight this information.
Do Clinical Trials Include Men and Women?
Some of the earliest clinical trials of PTSD psychotherapies focused on women who experienced rape. As trials turned to testing treatments among military Veterans with combat exposure, more men were included in research. Although women are slightly less likely to experience trauma in their lives, the prevalence of PTSD is slightly higher among women, and the types of traumatic events that are most likely to lead to PTSD (e.g., sexual assault, abuse during childhood) are more common among women. As with race and ethnicity, gender may affect treatment access, initiation and engagement. And with the inclusion of men and women in clinical trials, the field is beginning to learn how gender may impact how well treatments work.
Clinical Trials: Gender
In the PTSD-Repository, only a small portion, 6% of studies, do not include gender information for participants. As shown here, 13% of trials are limited to men, and 12% of studies included exclusively women. The large majority (69%) of trials include both men and women.
You can "drill down" in the pie chart by selecting a slice, which shows you which treatment types are represented in the studies of men, women or both. For example, among the 47 RCTs that are only women, most (36 RCTs or 77%) are psychotherapy trials. Among the 51 studies that are limited to men, there is more parity between psychotherapy (n=20, 39%) and pharmacotherapy (n=12, 24%) studies. Greater attention to medication trials with women will also help the field better understand risks to reproductive health and best practices for women of childbearing age.
Where in the World Are Clinical Trials Being Done?
The PTSD-Repository is limited to studies published in English. Almost two-thirds (64%) of RCTs included were completed in the United States, 15% were based in European countries and 10% are from the Middle East. Canada (n=7), Asia (n=10), South America (n=5), and Africa (n=3) are also represented. An additional 8 studies are international samples. Interact with the map below to view the number of studies specific to each country.
Clinical Trials: Map
Do RCTs Include Military and Community Participants?
The risk for trauma exposure in the military is significant and the willingness of Veterans and Service members to participate in research advances the field's knowledge of how treatments work in this population. Also, military-related trauma is not limited to combat, as accidents and sexual assault also occur; and, childhood trauma is more common among those who join the military. Veterans and Active Duty members who participate in RCTs allow us to learn more about how treatments work for military populations and extend that benefit to anyone who may ultimately need PTSD treatment.
Clinical Trials: Military & Community Samples
The majority of RCTs (54%) 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 32% of RCTs specific to Veterans and 3% limited to Active Duty. Only 9 studies in the PTSD-Repository did not report this information.
Interestingly, looking at Veteran-specific RCTs by study type (see below), complementary and integrative health (CIH) trials are more common than in community samples. Half of CIH studies are Veteran-only samples. This may reflect recent efforts by VA to better understand the efficacy of CIH for PTSD. Studies of nonpharmacologic cognitive interventions--teaching cognitive skills to improve attention--are also more common in Veteran samples (50%). Veteran samples also make up more than half (60%) 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. That said, it is important to be mindful that community samples may include military personnel who were either not asked about military service or did not report that experience.
Clinical Trials: Gender & Military
Interact with the pie chart to see how studies that have all male (13%) or all female (12%) samples vary by military status. Not surprisingly, the majority of RCTs limited to men (86%) 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--or number of all cumulative traumas or types of traumas experienced across a lifetime--as well.
Knowing information about the type(s) or number of traumas experienced by participants in treatment trials is valuable for at least 2 reasons. First, the type of trauma is important because we want to know if specific traumatic events are associated with different treatment outcomes. Early on researchers wanted to know if specific treatments worked better for particular trauma types. To date, data show that the most effective treatments work for all types of trauma.
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 findings are generalizable (applicable) in terms of treatment efficacy.
In the PTSD-Repository, most studies (85%) report some information about trauma exposure history. Assessing for trauma is part of the PTSD diagnostic practice; however, research participants may be included based upon self-report or review of medical charts (which may not include information about specific types of trauma(s) experienced).
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= 16 RCTs with a total of 1680 participants). Within the 36 studies that count number of traumatic events--some reporting multiple types of events, others reporting multiple events of the same type--the average is 7 traumas (n=36 RCTs with a total of 2642 participants). See the scatter plots below for more details.
The chart below shows RCTs that focused on specific trauma types by study class. The widest variety of types of treatment can be found among studies with military combat-exposed participants.
Are Clinical Trial Participants 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, or treatment naïve. This may be important because, for example, a study participant who did not benefit from previous treatments may have more persistent PTSD than a participant who is in treatment for the first time.
In the PTSD-Repository, 79% of studies do not report whether participants have a history of PTSD treatment. Of those that do report treatment history, only 3 RCTs focus on participants who are new to PTSD treatment, and all of these are psychotherapy studies.
It is more likely that when reported, participants in research studies are not new to PTSD treatment. If we look at those studies in which all participants report treatment history (meaning, the sample is 0% treatment naïve), about one-third of studies tested psychotherapy with another third of studies examining pharmacotherapy.
Among the 88 pharmacotherapy trials included in the PTSD-Repository, 85% did not report PTSD treatment history and of those that did, all include at least some participants with prior PTSD treatment. Almost three-quarters of pharmacotherapy RCTs that assess treatment history report that all participants in the given study have taken medications for PTSD (e.g., antidepressants) in the past.
How Common Are Co-occurring Conditions in Clinical Trials?
Over three-quarters of people with PTSD also have another disorder (Pietrzak et al., 2011). It is common for people who have PTSD to report having co-occurring conditions such as a history of traumatic brain injury (TBI), substance use disorder (SUD) or depression. These comorbidities are important considerations for treatment planning and can affect treatment engagement and response. 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 (89%). And, of those that do, participants with severe TBI history are generally excluded from the trial. There is one study in the PTSD-Repository focused on Veterans with co-occurring PTSD and TBI. Studies that combined psychotherapy & pharmacotherapy are more likely to assess for a history TBI (20% of them, compared to the 11% overall). Even among Veteran studies, only 14% report on TBI history, in part because participants with TBI were excluded.
SUD is another important co-occurring condition both in terms of 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. Learn more in our story, Treatments for Co-occurring PTSD and Substance Use Disorder.
Depression is common in people with PTSD, with the National Epidemiological Survey on Alcohol and Related Conditions (wave 2) reporting major depression co-occurring for 35% of those with PTSD, compared to a prevalence of 14% among those who do not have PTSD (Pietrzak et al., 2011). Most (60%) of the RCTs included in the PTSD-Repository do not report whether participants have depressive symptoms. In pharmacotherapy trials.
The studies included in the PTSD-Repository provide rich information about the participants who are included in clinical trials for PTSD. As researchers work to better understand treatment outcomes, a continued focus on many types of 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 thorough assessment and reporting of participants' demographic characteristics, trauma and treatment histories, and comorbidities.
Pietrzak, R. H., Goldstein, R. B., Southwick, S. M., & Grant, B. F. (2011). Prevalence and Axis 1 comorbidity of full and partial posttraumatic stress disorder in the United States: Results from Wave 2 of the National Epidemiologic Survey on Alcohol and Related Conditions. Journal of Anxiety Disorders, 25(3), 456-465. https://doi.org/10.1016/j.anxdis.2010.11.010
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/