Interpersonal Psychotherapy for Posttraumatic Stress Disorder

Included in Random Assignment (
N 
= 110)
Assigned to Prolonged 
Exposure 
(PE: N = 38)
Received PE (N = 36):
Assessed for eligibility (N = 1390) 
Assigned to Relaxation 
Therapy
(RT: N = 32)
Withdrew (N = 2)
Withdrew (N = 2)
Assigned to Interpersonal 
Therapy
(IPT: N = 40)
Withdrew (N = 2) 
Received IPT (N = 38)
Received RT (N = 30)
Completed PE (N = 27):
Did not respond (N = 10)
Responded (N = 17)
Did not complete  
(N
 = 
9)
Did not complete 
(N
 = 
9)
Did not complete 
(N
 = 
4)
Completed IPT (N = 34):
Did not respond (N = 10)
Responded (N = 24) 
Completed RT (N = 21):
Did not respond (N = 10)
Responded  (N = 12) 
Intakes (N = 335) 
Taking medication = 3; out of area = 3; not 
interested = 56; money = 1; PTSD not primary 
diagnosis = 132; medical condition = 5; bipolar = 5; 
substance abuse = 2; other = 18
Taking medication = 307; out of area = 57; age = 36;
not interested = 452; money-seeking = 116;
No PTSD = 10; phone dead = 151;
medical condition = 1; bipolar = 3; other = 147
Figure  1. 1.
  Consort diagram of study flow.

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Is Exposure Therapy Necessary to Treat PTSD? 
13
[SD = 8.4], and Relaxation Therapy 3.8 years [SD = 4.4]). Patients could choose 
male or female therapists (Markowitz et al., 2015).
The 110 study patients all had chronic PTSD and a minimum CAPS severity 
score of 50— indicating at least moderately severe PTSD. None was taking 
psychotropic medication, and outside treatment was prohibited during the 14 
weeks of the trial. The patients were highly traumatized and chronically ill 
(Tables 1. 3 and 1. 4), racially and ethnically diverse, and had a mean age of 
40.1 years. Only 15.5% were married or living with a partner, and only 36.4% 
were employed full- time (10.9% were students). Ninety- three percent reported 
interpersonal traumas— which tend to cause greater distress than impersonal 
traumas such as natural disasters (Kessler et al., 1995; Markowitz et al., 2009). 
More than half (58%) of patients reported chronic trauma (mean duration since 
primary trauma, 14.1 years [SD = 14.4]), including sexual (35%) and physical 
(61%) abuse. Thirty- six percent reported childhood or adolescent traumas. 
Three- quarters of patients had previously received psychotherapy, and nearly 
half had received pharmacotherapy for PTSD (Markowitz et al., 2015).
Table 1. 4 describes patients’ psychiatric debility. As anticipated, half had 
current comorbid major depression; one- third reported having had multiple 
depressive episodes. Nearly half met criteria for personality disorders, partic-
ularly paranoid, obsessive- compulsive, and avoidant.
Patients assigned to Prolonged Exposure attended a mean of 8.3 sessions 
(SD = 3.1) (a mean of 748 minutes [SD = 277] overall); IPT patients attended a 
mean of 12.6 sessions (SD = 3.4) (a mean of 630 minutes [SD = 69] overall); and 
Relaxation Therapy patients attended a mean 7.8 (SD = 3.5) sessions (a mean of 
667 minutes [SD = 290] overall), or 83%, 90%, and 78% of prescribed sessions, 
respectively.
Outcomes
CAPS scores substantially improved in each therapy over the 14- week course 
of treatment (Table 1. 5), with large within- group pre- treatment– post- treatment 
effect sizes (Cohen’s d): for Prolonged Exposure, 
d =
 1.88; for IPT, 
d =
 1.69; and 
for Relaxation Therapy, 
d =
 1.32. These changes indicate large reductions in PTSD 
symptoms in all three treatments. The time- by- treatment interaction was not sig-
nificant. In comparison with Relaxation Therapy, Prolonged Exposure showed a 
significant advantage (
p
 = 0.010), whereas IPT’s advantage fell short of statistical 
significance (
p
 = 0.097). 
Crucially, the between- group difference in CAPS change 
scores between Prolonged Exposure and IPT was 5.5 points, less than the 12.5- point 
minimal inferiority threshold that we had defined
 a priori. Thus the null hypo-
thesis of more than minimal inferiority of IPT was rejected (
p
 = 0.035) (Table 1.5).
 
 

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Table  1. 3.
  Demographic Characteristics of Patients with PTSD Receiving 
Prolonged Exposure, IPT, or Relaxation Therapy