Hello RoseStarBlue and thanks for posting,

Clinical trials look at a wide range of different things and as a result trial designs and entry requirements vary.  Trials are usually designed to obtain data to answer something specific and the trial design, including entry requirements, tend to reflect this so the data generated is unambiguous.

With trials investigating new treatments, I think if participants were to have several conditions possibly including different medications, the data that emerges might be less clear cut, but I suppose this would depend on what was being researched. Most probably the question about whether or not to include trial participants with co morbidities is a trial by trial consideration and I assume there could be exceptions, but this would depend on the specific trial.  

Get back to us if you need to and give us a ring if you want to talk anything over. Our number is 0808 800 4040 and we are around weekdays from 9-5. 

Al the best,

Julia