Actually, no study on earth has ever recorded the opinion that Trans lead unhappy lives; the entire spectrum of depression in Trans results in either A. Discrimination, B. Medical Health (hormonal imbalances that have caused a man or woman to look too extreme to transition realistically), C. Discrimination in the Medical Health field that restricts a Trans' health improvments. Trans' have indeed been proven to commit suicide more than almost any group of people on Earth, but those suicidal thoughts are directly the result of Discrimination and not the Disorder itself; even the DSM says this.
Absolutely no other factors have been recorded in Trans mental health. Even the sometimes Mental Health conditions, such as BDD, Phobias, ect ect, all have been proven to have been caused by earlier Discrimination or Abuse in a trans' life. Quite frankly, this very same thing has been proved in people of all genders or orientations, the psychology of it is really no different. Discrimination and Abuse causes Depression, there's hardly ever been a recorded instance where a person is Depressed without an underlining physical reason (though oftentimes these physical reasons are denied by Religious-based Therapists who insist that Depression is a root of Sin or Chemical Imbalance, when it is not.)
For instance, some professionals will claim that Depression happens because of a chemical imbalance. This is fraudulent and untrue. The Chemical Imbalance that can be read using technological advances is actually caused by persistent Depression, the Chemical Imbalance is not the cause, but the result. This resulting Chemical Imbalance, the result of Abuse and Neglect, can actually go on further to cause many Health Issues, so it's quite literally an emergency to fix Depression in a Realistic way (Social, Realistic Transitioning, Proper Image/ Gender Treatments). Anti-Depressants really just do not do anything that a good old shot of Whiskey doesn't do; who wants to stay drunk and high all the time to forget a physical problem in life?
Quite frankly, modern Anti-Depressants and the like did not exist until just decades ago, yet humanity has survived thousands and thousands of years by gulping down booze, being brain-washed by churches, and having sex every 4 seconds. It works just as much as any medication has proven to. Yet they both are dangerous, detrimental alternatives in the face of having your physical health issues, such as physical image, gender image, and gender identity fixed in a hormonal or surgical manner. Studies overwhelmingly prove that physical alternations to a person's physical issues results in more happiness, both short term and long term, than therapedic, depressant, or religious alternatives ever could.