Clinical perspective, offered as context rather than as advice. The version of this that has an answer is narrower than the version being asked. Narrow it and it becomes tractable; leave it broad and the thread will produce nine confident and incompatible replies.
If somebody has the primary source to hand I would rather cite it than paraphrase it.
OP back with an update, since a thread like this is useless without one.
Following this thread I went back and re-read the extension data properly. The point about trough rather than peak explains the pattern I was seeing on day six, which I had been blaming on the vial.
SleepDoc_PDX said:The version of this that has an answer is narrower than the version being asked.
Adding the part of the answer the thread has not reached. If two explanations both fit, the useful question is which one predicts something the other does not. That is answerable; arguing about which sounds more plausible is not.
Worth separating that from training through weight loss, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.
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Browse GL BiochemOne concrete data point for the thread. Say what you would expect to see if you were wrong, before you look. It is a small discipline and it changes what you notice.
A narrower follow-up, since the general answer is now clear:
How would you tell the difference between that and the alternative explanation?