From the members I have conversed with, they are forbidden from using caffeine.
> It took a great deal of time, repetition, patience; no small amount of hope and faith; lots of reassurance from my wife; and many liters of a diet soda that shall remain nameless.
[0] https://www.churchofjesuschrist.org/study/general-conference...
This is the type of black and white response that I find so common with ex-mormons. If somebody pushes back on disinformation (even easily disproved like the above thing about keeping caffeine teachings secret), the superstitious thinking kicks in and excuses fly (like "they must be a secret apologist" which I heard recently). It's every bit as ridiculous as the believers are when they dismiss inconvenient facts like Zelph the White Lamanite[1][2] because it goes against their preferred narrative. It's superstitious thinking.
Edit: Hah! I couldn't have asked for a better real-time example to demonstrate my point: https://news.ycombinator.com/item?id=35774479
The exmormon community is extremely thorough and factual when it comes to talking about the church, because it is to their benefit. More people have left the church after unsuccessfully trying to refute The CES Letter than have ever left due to smear campaigns and slander. The truth is to the rational thinker’s benefit, which is why the church spends so much time and money hiding it and whitewashing it.
For someone so committed to "truth", "rational thinking," and being "extremely thorough and factual" you've sure gotten a lot wrong in just this message. Mormonthink is far from a prominent apologist foundation. Most Mormons consider them anti. You should probably look at the site before jumping to such a confirmation-bias driven conclusion.