[redleader55]

Patients with incurable or hard to cure diseases are susceptibile to be exploited by companies or doctors that want to try unproven treatments on them. On the other hand, telling someone they are not allowed to do everything they can to save themselves is equally bad.

[RockRobotRock]

How can we collect useful data on experimental medicine outside of a controlled study?

[dredmorbius]

Centres of disease control (in the US and elsewhere) track morbidity and mortality on a wide range of conditions, which is one standardised answer to your question. There are also (a small number of) independent or unorthodox researchers who pursue specific avenues. You'll of course find the frauds amongst these (e.g., Andrew Wakefield, who promulgated anti-vax theories and falsified research toward same), but there are also notable medical advances which have emerged in such contexts, such as J. Robin Warren and Barry Marshall's identification of Helicobacter pylori as the principle cause of stomach ulcers, rather than stress:

Jessica Tanenbaum, "Delayed Gratification: Why it Took Everybody So Long to Acknowledge that Bacteria Cause Ulcers" (2005)

<https://www.jyi.org/2005-february/2005/2/9/delayed-gratifica...>