I understand why a placebo group is needed. What I don't understand is why a placebo group is needed in every clinical trial. There is so much placebo data available from all performed clinical tests ... why you need another placebo group data ? Can't scientist compare current test results versus past placebo tests results ?

A few days ago I read some test about curcumin or alpha-lipoic acid. It was tested on a group op Alzheimer's disease sufferers. The result of the study was that people taking this agent didn't decline at the same rate as a normal AD sufferer. BUT, the result was inconclusive because there was no placebo group involved. That's when I was thinking "Huh ? There have been performed so many placebo tests. Why don't you just compare the current results with past placebo results ?".

I'm not 100% sure (I've never set up a clinical trial) but I would think that the placebo group would go through the same procedure of the clinical trial as the experimental group (e.g. attending the same ward as the experimental group, given the same information and the same follow up procedure), the only difference (ideally) would be the medication or treatment.

This is important for trials that relying on a patient's testimony to assess the drugs effectiveness; "how do you feel?" is a highly subjective question. Imagine you were in the trial and you were told you were taking the experimental drug and then you were asked, "how do you feel?" You want the drug to work so you say its working or you try harder at a physical test. I guess it is easier when there is some sort of objective measure like a level of a protein in the body to measure effectiveness.

This makes it hard to assess the effectiveness of the drug. This might be compounded when comparing different studies because they may have used different procedures or formulations of the drug or different ways of administrating the drug or one was done in summer and the other in winter; any one of these differences may be causative.

Because clinical trials deal with unknowns, doctors don't know if the drug itself is effective so you have to control as many variables as possible and using previous placebo groups introduces unwanted variables. Its like the police are chasing a criminal through a train station. It is almost impossible to see the man running in the crowd. What the police need is for everyone else at the station to stand still. Only the criminal will be moving and therefore easily spotted

That's my thoughts anyway. Anyone else have any ideas?

dr jonny

dr jonny's right, I believe. The point of a randomised control trial (RCT) is that the control group is a random selection of the same cohort as the trial group, so that the only variable should be the drug taken. The importance of this is underlined if you note that placebo-takers will report many of the side effects that the drug takers report. So, in one study of Rasagline I think it was some 19% of drug takers who reported getting headaches (so headache is a "very common" side effect). But - 14% of placebo-takers reported headaches, too! It takes some sophisticated number-crunching to work out whether headaches then are statistically a significant side effect - which would be much harder or impossible to do if you didn't know the make-up of the cohort was a constant.

Incidentally, RCT might be the gold standard. But other trial procedures are available. i particularly like the relaxed-, if resignedly-sounding, Pragmatic Control trial.


That is my understanding too. I think the best results are obtained where neither the trial subjects nor the researchers taking the observations are aware of who is in the control group at the time of the trial. This prevents all manner of wishful thinking polluting the statistics.

Parkinson's UK is running a special lecture later this month about "Clinical Trials and Parkinson's"

Where : Royal Institution, London

When : 20 Nov 2013 1830 - 2000

Who : Dr Richard Wade Martins  &  Dr Alan Whone

Where do I sign up? :

It's free




I am going tomorrow to see my Parkinsons Nurse to go through an assessment which will take up to 2 hrs and will e over a period of 2 years. If I  am accepted I will assessed each time I visit the clinic, I must have a carer with me and I can withdraw at any time. I feel I should at least give it a try as my memory recall isn't very good.At the end of the day it's my decision and if it can help so be it.

Starting this thread, Mister X asked a good question: Why is a placebo group needed in every clinical trial? Note that he is not against taking into account the placebo effect. But, rather, he thinks that you can estimate it from previous trials.

The replies to his post offer good reasons as to why every trial benefits from having its own placebo branch. But, I don't think they go far enough to be conclusive.

First, cost v benefit. I see an argument against the current position is that it is too costly. Cheaper trials would allow the therapeutic value of more candidate drugs to be measured and the results to be found faster.

Second, the "product" that a person buys is not just the drug, but the packaging, the attention paid by doctors, the patients' expectation of the benefits of the drug, etc.. All of which go toward creating the placebo effect. So, it could be argued that a drug's direct impact plus the placebo effect is what should be tested. If this view is accepted, there is no need for a specific placebo group.


Hi all,

The placebo effect is an interesting phenomenon in which an inactive substance can sometimes make us feel better simply because we expect that it will.

This effect can cause problems in clinical trials as a drug could be seen to be effective just as a result of this phenomenon. Therefore often trials are ‘placebo-controlled’ whereby some participants receive a placebo and others will receive the real treatment. Performing trials in this way allows researchers to understand if people who have received the real treatment have done better than what would be expected just from the placebo effect. 

Why do we need a placebo group in each trial?

Every clinical trial is slightly different- involving different people, using different methods and looking at different outcomes to see if a drug or treatment is successful. Therefore the results for the placebo group will be specific to each trial and this would be hard to estimate. This is why a placebo group is needed for each clinical trial.

Also, drugs need to go through approval from regulatory agencies such as the MHRA and the EMA before they are made available to patients. These agencies look at clinical trial data to decide if a drug or treatment is both safe and effective for patients and they require placebo-controlled trials to make this decision. Therefore even if not having a placebo group could speed up a trial – it is less likely the drug would eventually be accepted by these agencies.

It is correct that other factors such as the way a medicine looks are thought to contribute to the placebo effect. In some clinical trials, including the GDNF trial, participants in the placebo group also receive the treatment after an initial period. This allows researchers to look at both the effect of the placebo and the treatment in the same participant.

We agree that clinical trials can work better and that is why we are working with drug companies, researchers and regulators as part of our Critical Path for Parkinson’s

Best Wishes,
The Research Team