I would like to see an example of previous trials where the placebo group was invalidated prematurely by informing them and giving them the actual drug. If this is common practice I'm not aware of it.
The use of placebos in controlled clinical trials must be justified by a positive risk-benefit analysis, and the subjects must be fully informed of the risks involved in the assignment to the placebo group.
Continued assignment of subjects to placebo is unethical, once there is good evidence to support the efficacy of the trial therapy.
Unfortunately (or fortunately) since there was such strong evidence to prove the efficacy, it became unethical for the continued assignment of placebo.
The good old "is unethical to do a double blind study". This one is by far the best invention of the Big Pharma PR departments, you basically cannot make the study that will prove for sure that their product is safe (and stick it to all those anti vaxxers once and for all) Talk about having your cake and eating it too...
Here's one. I'm sure you can find others ("terminated for benefit"). For statistical reasons, terminating a trial for benefit is relatively uncommon (most terminations occur for other reasons):
This happened with low-dose Aspirin for prevention of heart-attacks and strokes. The protective effect was so profound that they considered it unethical to let the control group proceed without it.
Surely the point of a placebo in this case was to measure effectiveness rather than detect long term side effects. There are other methods of establishing a control such as comparing to the general population.
Note the date on this article - this was back in February of this year: https://www.npr.org/sections/health-shots/2021/02/19/9691430...
Don't denigrate a perfectly valid criticism of deviations from historical norms of drug validation and approval by calling it a "conspiracy theory".