[Recently, I noticed I was approaching my 5,000 post. It came as a surprise, a pleasant surprise. I wanted the 5,000th post to be somewhat meaningful when along came this study. I hope it is of value. Have a great day and thank you Meso!] Onset Of Effects Of testosterone Treatment And Time Span Until Maximum Effects Are Achieved Treatment of hypogonadal men with testosterone is rewarding, for the patients as well as the physician. The patient experiences, to his satisfaction, profound changes in his physical appearance and his mental make-up. The attending physician observes the changes the patient undergoes and rarely fails to be fascinated by the multitude of functions testosterone appears to have in the process of masculinization in the broadest sense While the effects of testosterone have been described in detail, relatively little attention has been given to the time these effects take to occur and achieve a full expression. This seems relevant. To the attending physician, monitoring the effects of administration of testosterone will be facilitated when it is known when certain effects can and should be expected. Patients like to receive information when the effects will set in. Further, this information is relevant for the design of clinical trials on testosterone replacement therapy. It is important to have information when an effect can be expected and when its maximum has been attained. Saad F, Aversa A, Isidori AM, Zafalon L, Zitzmann M, Gooren LJ. ONSET OF EFFECTS OF TESTOSTERONE TREATMENT AND TIME SPAN UNTIL MAXIMUM EFFECTS ARE ACHIEVED. European Journal of Endocrinology. ONSET OF EFFECTS OF TESTOSTERONE TREATMENT AND TIME SPAN UNTIL MAXIMUM EFFECTS ARE ACHIEVED Objectives: Testosterone has a spectrum of effects on the male organism. This review attempts to determine, from published studies, the time-course of the effects induced by testosterone replacement therapy from their first manifestation until maximum effects are attained. Design: Studies in PubMed on testosterone replacement so far providing information on time course. Results: Effects on sexual interest appear after 3 weeks plateauing at 6 weeks, no further increments beyond. Changes in erections/ejaculations may require up to 6 months. Effects on quality of life manifest within 3-4 weeks, but maximum benefits take longer. Effects on depressive mood appear after 3-6 weeks with a maximum after 18-30 weeks. First effects on erythropoiesis after 3 months, peaking at 9-12 months. Prostate specific antigen and volume rise, marginally, plateauing at 12 months; further increase related to aging rather than therapy. Effects on lipids appear after 4 weeks, maximal after 6-12 months. Insulin sensitivity may improve within few days, but effects on glycemic control become evident only after 3-12 months. Changes in fat mass, lean body mass and muscle strength occur within 12-16 weeks, stabilize at 6-12 months, but marginally continue to improve over years. Effects on inflammation occur within 3 to 12 weeks. Effects on bone detectable after 6 months but continue at least for 3 years. Conclusion: the time-course of the spectrum of effects of testosterone shows considerable variation, probably related to pharmacodynamics of the testosterone preparation. Genomic and non-genomic effects, androgen receptor polymorphism and intracellular steroid metabolism further contribute to such diversity.