Is it good to recycle?

One common recruitment technique utilized by pretty much every research site is the recycling of research participants, but is this really a good thing?  On the one hand people who have participated in multiple studies are experienced in the conduct of trials, are aware of the time commitments, and most importantly are aware of the their obligations to report medication/health changes.  On the other hand, research naive participants have not been exposed to an investigational product before and may actually have a keener sense of changes to health/behavior that might be cause by a new drug or device.

Even though these investigational products have been evaluated to the point where metabolization rates are known and subjects are prohibited from participating in a study at least 30 days following previous study completion, I feel that any participation within the past 6 months or so could be grounds for disqualification from a trial.  This is for a couple reasons.  The first is that these drugs are still under development.  Even though researchers know a lot about their metabolism, it would make sense to me to wait much longer than necessary before allowing participation in another clinical trial just to err on the side of caution.  Imagine the situation if a subject finished one trial, waited 30 days, and then jumped on board with another trial, only to develop some nasty adverse event.  Seems obvious that the first investigational drug didn't cause the reaction because of the length of time between trials, but how can we be sure?...I mean the drug is still being researched and even if we're talking about a Phase IV trial, scientists are still learning about the drug.  Better to wait extra long than risk it, in my opinion.

The second reason is logistical.  If a study prohibits those people from participating in a previous trial only within the past month, participants would be more likely to jump from trial to trial in search of a better treatment or money.  I have seen it before where a subject is enrolled in a trial and loses interest (could be because he/she finds about a different study in which she might be interested) in the study before completion.  The subject discontinues prematurely, only to jump over to another trial at the conclusion of that 30 day period.  If the minimum wait time was a mandatory 6 months after receiving an investigational product, people might think twice about discontinuing for that reason or, hopefully, signing consent for the study in the first place.  Some studies actually do use more stringent rules for determining the eligibility of previous research participants, but that certainly isn't the norm because a lengthy wait time hinders enrollment to a certain degree (and of course if enrollment is slowed by even 1 subject, money is wasted).

I believe the entire industry would benefit from tighter restrictions on participation in multiple clinical trials, but unfortunately the number of people willing to participate in any study needs to grow considerably before this would even be considered.