@velvetdemon I'm doing a full reply because I want to give this question the time and space it deserves, and I really do appreciate your curiosity about this.
The short answer: It is deeply unethical. There are nowhere near enough willing patients in the world to be able to do this, and it would be criminal to put them through this.
The long answer: The one side of the equation you're focusing on is: how much of a drug is too much, to the point where it will cause negative side effects or even death? And this is crucial to know. But it's not just a matter of finding out the lethal dosage of a heart cholesterol medication, you need to know that it can actually lower the cholesterol of any living thing. There is no way to know this without giving it first to...a living thing.
But beyond this, I need to emphasize: The goal of a drug trial is to effectively cure people who are already suffering from disease, who are living on limited time.
Drug trials don't just happen on any member of the public, they need to happen specifically on people affected by the disease you're trying to treat. There is at any time a very limited and very marginalized population of the world affected by early onset, familial Parkinson's disease. Because you cannot ethically induce disease in a human being, you are working with, speaking with, and helping patients and their families who are hopeful and desperate for a cure.
If you were to jump straight to human trials from petri dishes, not knowing absolutely anything about how the drug functions in a living, breathing animal body, it would look like this:
- We didn't know that minute quantities of the drug interact lethally with x, y, z medication that people are commonly also taking. X number of patients have died as a result.
- We didn't know that the drug is fatal to people with [common variant] in their genetics. X more patients have died.
- We didn't know the drug exacerbates x, y, z chronic illnesses. X number of people have acquired permanent, lifelong disabilities.
- We didn't know the best way to deliver the drug, so we tried multiple ways: the people who received it intravenously are now suffering from a painful, costly, and debilitating condition that did not happen with the ingested form.
I could go on, and on, and on.
The vast majority of these problems can be nearly or almost entirely averted by testing other animals first.
These are all people who possibly could have waited for the normal progression from animal testing to human testing and thus received better outcomes. Some people will pass away in the time it takes to get to that point, and that's heartbreaking, and we all wish science could be faster.
But the cost of expediting science could mean a life of profoundly greater suffering or an even shorter life than the one where no intervention happens at all. And at that point, you have completely exhausted your trust, your goodwill, and your patients' hope, after you've failed to do anything or even worsened the lives of people who are already deeply suffering.
