Transdermal Testosterone is a just another testosterone- typically a lower dose –that is administered in an entirely different way. Transdermals are applied as a patch on the skin, typically using a low, dry heat to attach the patch, or in gel form that is directly applied on the skin.
Originally, testosterone therapy was used in the past fifty years to treat hypogonadism – a reproductive disorder wherein the gonads (ovary for women and testes for men) fail to produce hormones (testosterone, estradiol, etc.) or gametes (sperm or egg cells) - via oral or intra-muscular administration. Later on, when studies found that declining hormone levels on pre-menopausal women results in hormone withdrawal symptoms that affect moods, well-being and sexual functioning, Hormone Replacement Therapy (HRT) was introduced, which include testosterone replacement and best steroids for weight loss (as women also stores minute but essential amounts of the male hormone testosterone). When late-onset hypogonadism (andropause or male menopause) was recognized, HRT was extended to men as well.
Transdermal testosterone was created to address the need for more practical and convenient delivery of the hormone: oral therapies aren’t advised because of hepatoxic effects of the compound which have to be altered at the 17th carbon atom to survive the first pass at the liver (liver toxicity is a special concern especially as patients are mostly past middle-age and are no longer in pink health). Similarly, intra-muscular injections aren’t that welcome body builder on steroidsdue to the complications relating to injections, such as lumps and abscesses and even HIV contamination. Applying the drug through the skin (transdermal) either as a patch or a gel, therefore, was a welcome development for those who need testosterone replacement therapy. Transdermal testosterone comes in two types: scrotal (applied directly to a shaved part of the scrotum) or non-scrotal (applied to areas other than the scrotum). Scrotal patches were found to be more beneficial as high levels of circulating dihydrotestosterone (DHT) are produced due to the high 5-alpha-reductase enzyme activity of scrotal skin .
Before long, bodybuilders and athletes who are using oral and injectable testosterone got interested in the transdermal form, primarily due to the relatively easy way to get the drugs and the high probability of escaping detection. Transdermal testosterone abuse was highlighted by the BALCO scandal wherein the newly-engineered "The Cream" was used to introduce testosterone by rubbing on the skin which resulted in trimming body fat and building muscle for the client athletes of BALCO.
While transdermal systems are less potent than injected testosterone, the skin administered drug shows more stable blood plasma levels  than an injectable, though the latter has much higher peak plasma concentrations. In short, concentration of testosterone in the blood is more constant, whereas it shoots up spectacularly and declines as rapidly when injected.
In the same study, it was found that sexual function and mood parameters of the subjects were comparable with the patients’ previous intra-muscular treatment regimens, and there were no statistically significant differences between groups. Other parameters in the study such as adverse effects of testosterone administered through injection and transdermal system on the liver, prostate, lipid profile and hematocrit were also found to be the same regardless of its delivery . Clearly, transdermal testosterone is a good alternative for the traditional delivery methods and has its own advantages.