Nearly all credible clinical research nowadays is “double blind”, because it’s too easy for the researchers to skew the results if they know who’s getting the placebo. Meaning, even the researchers don’t know who’s getting what. At least not the ones with any patient/data contact.
Whatever safety protocols are in place for those taking immunosuppressants would also apply to those on the placebos. Every single person is subject to the rules.
Whether or not one should be taking immunosuppressants during a pandemic is a valid concern, though, and I would assume largely part of why @Timothy posed the original question.
This has been studied, and hospitalized covid patients taking immunosuppressants do not fare any worse than those who are not. The most serious side-effects of Covid-19 are actually caused by our own immune systems attacking the virus, and our own cells where the virus lives. Thus, slowing down immune response might mean it takes longer to fight off the virus, but one should not be (more?) seriously ill while doing so. Of course, with all things Covid-related, prevention in the first place is still the best medicine.
There are quite a few other concerns that might be deal-breakers when it comes to the possibility of taking immunosuppressants, but Covid alone shouldn’t top that list.
Remember too, researchers cannot ethically (or legally for that matter) expect you to continue any experimental therapy if you’re experiencing severe side effects. They might ask you tough out minor pain, nausea, and the like, but treatment can be discontinued at any time if you’re experiencing severe distress of any sort. You can even voluntarily drop out of the study if they don’t choose to stop treatment themselves.
This would be top of my further questions… What have previous outcomes and side effects looked like. Prevalence of side effects, minor and major, and how comfortable are you knowing that’s the likelihood you’ll experience the same… and what criteria they have for aborting treatment. Also, if there is compensation for participation, what penalty is there for voluntarily dropping out. Payments are often incremental. What happens if you’re forced to drop out because of side effects? Do they remove the capsules of stem cells? Can you switch to the other therapy option? (Would invalidate your results, but maybe there are side effects to NOT taking the immunosuppressants and you’d fare better with them afterall)