Currently available testosterone preparations in common use include intramuscular injections, subcutaneous pellets, buccal tablets, transdermal gels and patches (see Table 2). Oral testosterone is not widely used. Unmodified testosterone taken orally is largely subject to first-pass metabolism by the liver. Oral doses 100 fold greater than physiological testosterone production can be given to achieve adequate serum levels. Methyl testosterone esters have been associated with hepatotoxicity. There has been some use of testosterone undecanoate, which is an esterified derivative of testosterone that is absorbed via the lymphatic system and bypasses the liver. Unfortunately, it produces unpredictable testosterone levels and increases testosterone levels for only a short period after each oral dose (Schurmeyer et al 1983).
Think: when you were teenager: you were active without thinking of ways to be active. When you start TRT, you want to be mobile/active (maybe again), don’t forget this when you stop TRT. You have to think of ways to incorporate activity into your routine or you get porky.When you cycled, walked everywhere as a teen you did this automatically. Without the hormone stimulus you must use your head and memories of what to do. here’s where the memory issue occurs.

If a man's testosterone looks below the normal range, there is a good chance he could end up on hormone supplements—often indefinitely. "There is a bit of a testosterone trap," Dr. Pallais says. "Men get started on testosterone replacement and they feel better, but then it's hard to come off of it. On treatment, the body stops making testosterone. Men can often feel a big difference when they stop therapy because their body's testosterone production has not yet recovered."
If low T is your initial concern, lifestyle changes may help. “Dietary and exercise changes, particularly limiting sugars, especially fructose, eating healthy saturated fats, and engaging in high-intensity exercises may relieve symptoms of low testosterone," Lucille says. "Strength training, reducing stress, and optimizing vitamin D levels can also be very effective at boosting testosterone levels naturally."
“However, the parallels don’t necessarily follow logically, creating a real need to bring more evidence to this area so that physicians and patients would be able to make more  informed decisions based on the best possible evidence,” said Dr. Gill, a professor of medicine and the lead investigator at the Yale study site, the largest site participating in the TTrials, and coauthor of all 4 TTrials. 
Testosterone increases the tolerance for risk-taking. Testosterone has a strong link with one’s willingness to take risks. Studies show that men with low levels of power and status, but high levels of T, are motivated to take risks in order to gain status and power. On the other hand, men with high T, who already have power and status, are more risk-averse, because they want to hold on to what they have.
Some of these signs and symptoms can be caused by various underlying factors, including medication side effects, obstructive sleep apnea, thyroid problems, diabetes and depression. It's also possible that these conditions may be the cause of low testosterone levels, and treatment of these problems may cause testosterone levels to rise. A blood test is the only way to diagnose a low testosterone level.