A healthcare provider will usually give you this injection in a hospital or clinic setting. Testosterone is a hormone that your sex organs mainly produce. Testosterone replacement therapy may be an option for you. But there aren’t many studies on the long-term effects of TRT (for example, over decades). Once you start TRT, you’ll have regular appointments with your healthcare provider and routine blood tests. Your body will take some time to restart production of testosterone naturally. Many men enjoy the routine of daily injections — they take pride in their discipline and often feel a sense of control knowing their levels stay consistent. Each testosterone injection raises your blood levels and then gradually drifts down as the hormone is metabolized. Standard injection schedules like weekly or biweekly dosing are widely used because they are simple and effective for many patients. After your injection, testosterone levels rise and you may feel energized, focused, and more like yourself. The main difference between these routines is how much your testosterone levels rise and fall between injections. Longer gaps between injections can lead to more noticeable fluctuations, which is why some patients feel strong early on and less so later in the dosing cycle. When evaluating testosterone replacement therapy (TRT) protocols, the stability of serum hormone levels across different injection schedules is a critical factor influencing therapeutic efficacy and patient outcomes. Clinical evidence suggests that weekly injections maintain serum testosterone within the physiological range, minimizing symptomatic fluctuations and optimizing symptom control. Testosterone injections introduce exogenous testosterone directly into the systemic circulation, bypassing hepatic first-pass metabolism and enabling controlled elevation of serum testosterone levels. These large fluctuations in serum testosterone over a 2-week period illustrate the less-than-ideal kinetics of TC IM injections. A PK study (Nankin HR 1987) evaluated serum levels of testosterone periodically for 14 days after administration of TC 200 mg IM in 11 hypogonadal men (Reference). The best injection frequency depends on how your body absorbs and responds to the medication, as well as how stable your hormone levels remain over time. There’s no one-size-fits-all schedule when it comes to testosterone injections. Cypionate or enanthate ester-based formulations were originally labelled for administration every two to three weeks, but newer evidence suggests shorter intervals often provide more consistent results. Some men feel great for a few days, then experience fatigue or irritability as levels decline. This was confirmed by pharmacokinetic studies that assessed the Cmax and tmax of testosterone in the serum, and the average serum total testosterone concentration during the steady state. As discussed, SC administration of testosterone esters should result in a more stable absorption and release of testosterone into the circulation due to less fluctuation of lymphatic flow in the hypodermis with physical activity. As the lymphatic drainage from SC tissue is largely dependent on intrinsic pumping, while IM lymphatic flow is also substantially influenced by extrinsic pumping during physical activity (43), these drainage patterns suggest that testosterone esters administered SC likely have more stable absorption kinetics compared to IM administration. Molecules smaller than 1 kDa, such as testosterone, are preferentially absorbed by the blood capillaries because of the high rate of filtration and reabsorption of fluid across vascular capillaries (39). After IM or SC administration of a testosterone ester, absorption occurs first by diffusion from the depot into the interstitium (Fig. 2B). For testosterone esters, the time corresponding from administration to the Cmax, that is, time of maximum concentration (tmax), is determined by the rate at which absorption occurs, since the systemic elimination of testosterone is the same regardless of the route of administration. B, Schematic illustration of the absorption steps of testosterone esters after intramuscular (left) or subcutaneous (right) injection.
