system
Given the following post, respond as if you're commenting on Reddit:
human
CMV: The lack of long-term studies on the efficacy of transgender hormone therapy is a notable concern

EDIT 4 (read this): This topic was originally about a specific point of contention, but it became more about the overall process of making decisions regarding medicine. Some clarification:

(I am not trying to soapbox; I am explaining my full, refined position after awarding deltas, for any lurkers or future commenters)

Coming into this, I personally supported (and do support) hormone therapy, due to my own experience of the hellish alternative of dysphoria (I sympathize with the suicide attempt rates, because I happen to be one of them). From a purely rational stance, however, I was a bit of a fence-sitter with hormone therapy.

While my belief in the lack of long-term studies hasn't changed (there *are* some, but few), my belief in how it relates to the choice of transitioning (for myself and others) has.

Practical decisions, including those made in medicine, are about trade-offs. The side-effects of a treatment may be bad (not that I believe that is true for hormone therapy), but a choice could still be made to use said treatment if the alternative, not being treated, is worse.

The belief I started with was that there *may* be very bad long-term side effects of hormone therapy that are not known about. A combination of factors that led me to believe that the risk of this was minimal, and that it should not be a significant reason why one would not receive this treatment. Here are some (not all), in no particular order:

1. There are no anecdotes of severe long-term side effects, despite the length of time cross-sex hormone has existed. If any such effect existed, I would expect at least one case to be reported.
2. Short-term (<= 10 year) studies on side effects show relatively minimal effects. Cancer and various cardiovascular issues are the main two, and both of these are not far off typical occurrence rates among the population. (There is more nuance to this, but I want to keep this somewhat concise.)
3. Many treatments (particularly medications) are regularly used despite a lack of long-term evidence, because the short-term evidence was strong enough. These medications have not run into issues with long-term effects, as far as I know, and provide great benefit to people.
4. It is erroneous to assume that a lack of information on long-term outcomes would imply a notable possibility of negative risks over the long-term. This is a bit hard to explain, since it is about the probability of a risk factor (aka probability of a probability), and starts to fall into more complicated questions of philosophy.
5. De-transitioning (without intent to re-transition) isn't *that* bad. I'm not minimizing or invalidating the experience of those who do, since I'm sure it really does suck. On a population scale, however, the total number these people comprise is small (averaging 1% or so), and the residual effects of hormone therapy are manageable.  
The absolute worst case scenario is that one starts their first puberty on cross-sex hormones, gets various surgeries, and then realizes this isn't for them (*This is a fringe case, not a representative sample of those who de-transition*). Given that their body is effectively typical for the their non-natal sex, transitioning back to their natal sex (or to a more androgynous state) would be similar to the experience of a typical trans person being denied treatment until a later age.  
Simply put: the worst outcome regarding one who de-transitions is nearly equivalent to the outcome of a trans person denied treatment until a later age (such a person *could* have an increased risk for certain complications, which is why I put *nearly*). Best-case scenario is little to no long-lasting effects. Given the exceptionally low de-transition rate (0% to 2%, depending on the study), this should not be too much of an issue.  
I hope that made sense, lol.
6. Other reasons, too, that I don't have all eternity to type out or remember.

Original post:

Clarification: I am *not* saying that hormone therapy should not be used as treatment; I am saying that this specific point is notable and should be considered when discussing hormone therapy.

I have spent quite a lot of time exploring research on the efficacy of hormone therapy. The research I have seen overwhelmingly supports the positive effects of transgender hormone therapy in time scales of less than 10 years after starting. I have typically given some leniency to the lack of long-term (greater than 10 years) evidence based on the difficulty of carrying out such studies and the strength of evidence in the short-term.

Recently, however, it has been brought to my attention that the longer (3-5 years) short-term studies suffer from high lost to follow-up rates, making them quite unreliable. I have heard proposals that there is a "honeymoon phase" after starting hormone therapy that can cause a temporary increase in mood, etc. I take the idea of a honeymoon phase with a degree of skepticism, however, given that it could be nothing more than some rationalization for a transphobic viewpoint, but what concerns me is the lack of evidence against it.

EDIT: I want to understand why the current state of long-term studies in not a concern when considering the efficacy transgender hormone therapy.

EDIT 2: When I say that the lack of long-term studies is a concern, I am saying that the lack of long-term studies means that tendencies of long-term outcomes are unknown. This unknown carries a risk of a negative outcome, which is a concern.

EDIT 3: My mind has been changed quite a bit on this matter. Thanks for the responses. It turns out that the lack of long-term studies is quite common and not that much of an issue with regard to most treatments, although they are helpful when they do exist. It's about working with the information there is and making a choice between the cost of the risk versus benefit of waiting for more information.
gpt
Reading online is not the path to understanding the best way to treat people who are trans. Either side (one that hormone therapy should be banned, the other that it should be put in the drinking water or whatever) are talking past a) the work of physicians who, like or not, often have a better chance at finding the right treatment than the Wikipedia surfer and b) the prospective patients themselves who are ultimately responsible for their own path in life. There are some side effects to some treatments, but that doesn't mean anything to people beyond individual patients and individual doctors. We don't whole-cloth argue against treatment for depression or for cancer because of the well-known side effects to those treatments. There's no reason for society to consider hormone therapy differently.