Clinical Drug Trials, PTSD and SSRIs

Travis DixonAbnormal Psychology, Biological Psychology, Research Methodology

Understand how clinical drug trials work is essential when evaluating the effectiveness of biological treatments for disorders like PTSD.

This post is designed to be used in lesson 4.6 in the PTSD unit plan.

In order to evaluate the effectiveness of drug therapy using selective serotonin reuptake inhibitors (SSRIs) to treat PTSD, we need to consult the research.

The most common way the effectiveness of drugs are tested is through a carefully controlled experiments. These experiments are also known as “clinical trials” when the independent variable is a medical treatment.

Random-allocation, double-blind, placebo-controlled clinical drug trials

These experiments follow some pretty standard procedures:

  • Participants are gathered. With studies on SSRIs and PTSD, the participants will be people with PTSD, often with a similar traumatic experience (e.g. veterans).
  • Data is gathered about their current symptoms or behaviours (so they can measure the change). In PTSD, the CAPS (Clinically Administered PTSD Scale) interview is used to measure symptom severity.
  • They are then randomly divided into one of two conditions: the treatment group (receives the SSRI drug) and the control group (receives a placebo treatment).
  • The studies are “blind” because the participants don’t know which group they’re in. If they’re “double-blind” it also means that the researchers giving the medication and collecting data also don’t know which group they’re in.
  • They take the drug for a certain period of time (e.g. 12 weeks).
  • The effects of the treatment/placebo are measured by gathering data at a second point.
  • Comparisons are made between the changes in behaviour between the two groups. If the treatment (SSRI) has a significant difference in effectiveness, it can be concluded that the drug is effective.


Marshall et al. (2001) conducted a random-allocation, double-blind, placebo-controlled experiment on 551 patients with PTSD. They had 12 weeks of treatment with either the SSRI paroxetine or placebo. (Actually, there were two paroxetine conditions with one group receiving 20mg per day and another 40mg per day). They measured the CAPS scores before and after and found that the paroxetine significantly reduced the symptoms more than the placebo group.

As with many drugs, there were some side-effects reported, including nausea, diarrhea and somnolence (feeling sleepy and drowsy).

This study gives one piece of simple evidence to use when evaluating the effectiveness of SSRIs. However, MacNamara’s study included in the textbook is far more valuable.

This video from SimpleLearningPro gives a good overview of how and why experiments use placebos and treatments in double-blind experiments.

NOTE: The content in this post could also be applied to topics in the biological level of analysis, including neurotransmission, ethical considerations and research methods.

Video: When drug trials go wrong – this is a fascinating example of the dangers and ethical issues involved in drug trials.