A placebo control is not a placebo effect

Following up on yesterday's post regarding a study of placebo-related information, it seems worthwhile to pause and expand on the difference between placebo controls and placebo effects.

The very first sentence of the study paper reflects a common, and rather muddled, belief about placebo-controlled trials:

Placebo groups are used in trials to control for placebo effects, i.e. those changes in a person's health status that result from the meaning and hope the person attributes to a procedure or event in a health care setting.

The best I can say about the above sentence is that in some (not all) trials, this accounts for some (not all) of the rationale for including a placebo group in the study design. 

There is no evidence that “meaning and hope” have any impact on HbA1C levels in patients with diabetes. The placebo effect only goes so far, and certainly doesn’t have much sway over most lab tests.  And yet we still conduct placebo-controlled trials in diabetes, and rightly so. 

To clarify, it may be helpful to break this into two parts:

1. Most trials need a “No Treatment” arm. 
2. Most “No Treatment” arms should be double-blind, which requires use of a placebo.

Let’s take these in order.

We need a “No Treatment” arm:

• Where the natural progression of the disease is variable (e.g., many psychological disorders, such as depression, have ups and downs that are unrelated to treatment).  This is important if we want to measure the proportion of responders – for example, what percentage of diabetes patients got their HbA1C levels below 6.5% on a particular regimen.  We know that some patients will hit that target even without additional intervention, but we won’t know how many unless we include a control group.
• Where the disease is self-limiting.  Given time, many conditions – the flu, allergies, etc. – tend to go away on their own.  Therefore, even an ineffective medication will look like it’s doing something if we simply test it on its own.  We need a control group to measure whether the investigational medication is actually speeding up the time to cure.
• When we are testing the combination of an investigational medication with one or more existing therapies. We have a general sense of how well metformin will work in T2D patients, but the effect will vary from trial to trial.  So if I want to see how well my experimental therapy works when added to metformin, I’ll need a metformin-plus-placebo control arm to be able to measure the additional benefit, if any.

All of the above are especially important when the trial is selecting a group of patients with greater disease severity than average.  The process of “enriching” a trial by excluding patients with mild disease has the benefit of requiring many fewer enrolled patients to demonstrate a clinical effect.  However, it also will have a stronger tendency to exhibit “regression to the mean” for a number of patients, who will exhibit a greater than average improvement during the course of the trial.  A control group accurately measures this regression and helps us measure the true effect size.

So, why include a placebo?  Why not just have a control group of patients receiving no additional treatment?  There are compelling reasons:

• To minimize bias in investigator assessments.  We most often think about placebo arms in relation to patient expectations, but often they are even more valuable in improving the accuracy of physician assessments.  Like all humans, physician investigators interpret evidence in light of their beliefs, and there is substantial evidence that unblinded assessments exaggerate treatment effects – we need the placebo to help maintain investigator blinding.
• To improve patient compliance in the control arm.  If a patient is clearly not receiving an active treatment, it is often very difficult to keep him or her interested and engaged with the trial, especially if the trial requires frequent clinic visits and non-standard procedures (such as blood draws).  Retention in no-treatment trials can be much lower than in placebo-controlled trials, and if it drops low enough, the validity of any results can be thrown into question.
• To accurately gauge adverse events.  Any problem(s) encountered are much more likely to be taken seriously – by both the patient and the investigator – if there is genuine uncertainty about whether the patient is on active treatment.  This leads to much more accurate and reliable reporting of adverse events.

In other words, even if the placebo effect didn’t exist, it would still be necessary and proper to conduct placebo-controlled trials.  The failure to separate “placebo control” from “placebo effect” yields some very muddled thinking (which was the ultimate point of my post yesterday).

The Placebo Effect (No Placebo Necessary)

4 out of 5 non-doctors recommend starting
with "regular strength", and titrating up from there...
(Photo from inventedbyamother.com)

The modern clinical trial’s Informed Consent Form (ICF) is a daunting document.  It is packed with a mind-numbing litany of procedures, potential risks, possible adverse events, and substantial additional information – in general, if someone, somewhere, might find a fact relevant, then it gets into the form.  A run-of-the-mill ICF in a phase 2 or 3 pharma trial can easily run over 10 pages of densely worded text.  You might argue (and in fact, a number of people have, persuasively) that this sort of information overload reduces, rather than enhances, patient understanding of clinical trials.

So it is a bit of a surprise to read a paper arguing that patient information needs to be expanded because it does not contain enough information.  And it is yet even more surprising to read about what’s allegedly missing: more information about the potential effects of placebo.

Actually, “surprising” doesn’t really begin to cover it.  Reading through the paper is a borderline surreal experience.  The authors’ conclusions from “quantitative analysis”* of 45 Patient Information Leaflets for UK trials include such findings as

• The investigational medication is mentioned more often than the placebo
• The written purpose of the trial “rarely referred to the placebo”
• “The possibility of continuing on the placebo treatment after the trial was never raised explicitly”

(You may need to give that last one a minute to sink in.)

Rather than seeing these as rather obvious conclusions, the authors recast them as ethical problems to be overcome.  From the article:

Information leaflets provide participants with a permanent written record about a clinical trial and its procedures and thus make an important contribution to the process of informing participants about placebos.

And from the PR materials furnished along with publication:

We believe the health changes associated with placebos should be better represented in the literature given to patients before they take part in a clinical trial.

There are two points that I think are important here – points that are sometimes missed, and very often badly blurred, even within the research community:

1.    The placebo effect is not caused by placebos.  There is nothing special about a “placebo” treatment that induces a unique effect.  The placebo effect can be induced by a lot of things, including active medications.  When we start talking about placebos as causal agents, we are engaging in fuzzy reasoning – placebo effects will not only be seen in the placebo arm, but will be evenly distributed among all trial participants.

2.    Changes in the placebo arm cannot be assumed to be caused by the placebo effect.  There are many reasons why we may observe health changes within a placebo group, and most of them have nothing to do with the “psychological and neurological mechanisms” of the placebo effect.  Giving trial participant information about the placebo effect may in fact be providing them with an entirely inaccurate description of what is going on.

Bishop FL, Adams AEM, Kaptchuk TJ, Lewith GT (2012). Informed Consent and Placebo Effects: A Content Analysis of Information Leaflets to Identify What Clinical Trial Participants Are Told about Placebos. PLoS ONE DOI: 10.1371/journal.pone.0039661

(* Not related to the point at hand, but I would applaud efforts to establish some lower boundaries to what we are permitted to call "quantitative analysis".  Putting counts from 45 brochures into an Excel spreadsheet should fall well below any reasonable threshold.)

DIA: Tutti, ma non troppo

I will be at DIA 2012 this week, and hope to post about sessions and new offerings of interest as I encounter them.

There is an inherent tension in this year’s meeting theme, “Collaborate to Innovate”. Collaboration at its best exposes us to new ideas and, even more importantly, new ways of thinking. That novelty can catalyze our own thinking and bring us to flashes of insight, producing creative solutions to our most intransigent problems.

However, collaboration often requires accommodation – multiple stakeholders with their own wants and needs that must be fairly and collectively addressed. Too often, this has the unfortunate result of sacrificing creativity for the sake of finding a solution that everyone can accept. Rather than blazing a new trail (with all its attendant risks), we are forced to find an established trail wide enough to accommodate everybody. Some of the least creative work in our industry is done by joint ventures and partnered programs.

So perhaps the best way forward is: Collaborate, but not too much. We must take time to seek out and integrate new approaches, but real breakthroughs tend to require a lot of individual courage and determination.