Clostebol is a synthetic anabolic-androgenic steroid, a derivative of the natural hormone testosterone. Clostebol is a Schedule III controlled substance used medically in topical ophthalmologic and dermatologic treatments. Due to potential use as a performance-enhancing drug, clostebol is banned by the World Anti-Doping Agency.

Clostebol:
https://drugs.ncats.io/drug/Z7D4G976SH

Clostebol is an old anabolic steroid that wasn't very popular outside of the former German Democratic Republic. The original German version of Clostebol was available in both the oral form (a 30 pill box with 15mgs/pill) and injectable form (a 1.5ml vial that contained 10mgs). There is no difference between the two versions other than one being a solid and the other being a liquid. Testosterone, of course, is available with methylation for oral use, as well as a variety of esters for injection. But with testosterone, we are talking about the most commonly prescribed anabolic steroid in the world, and literally zero pharmaceutical firms produce it with the same ester for oral as well as injectable use. Therefore, Clostebol (which is just testosterone with a 4-chloro substitution), is considerably unique in the fact that it utilizes the same ester for both injectable and oral use. This also makes it harder to detect as an oral, as it doesn't produce long-acting methylated metabolites.

However, the German version is no longer produced, nor is Steranabol an Italian version of the product. In practical terms, the legitimate pharmaceutical preparations of clostebol were expensive, inadequately dosed, and not very popular for athletes outside of Germany (obviously that last statement has changed in recent years).

Clostebol (once again, and not considering the ester) is simply testosterone with a 4-chloro substitution in the A-Ring. This has the effect of preventing aromatization, which is the conversion of testosterone to estrogen. So, in the simplest of terms, what we are looking at is a form of testosterone that doesn't convert to estrogen. While this might sound great, it's important to note that the conversion of testosterone to estrogen actually imparts many beneficial effects, not the least of which is an increased anabolic (muscle-building) capacity. Of course, there are a lot of potential drawbacks to steroids that convert to estrogen, not the least of which are gynecomastia (development of female-like breast tissue), water retention, and additional/increased suppression of natural testosterone levels. That last side-effect occurs with every steroid, but it seems to be worse with the ones that have a high rate of conversion to estrogen.

Also of note is that the oral form of Clostebol isn't really liver-toxic. Clostebol has been compared to milder steroids such as Primobolan. Clostebol isn't the first choice for professional bodybuilders, powerlifters, strongmen, or anyone needing huge amounts of mass or strength (and not subject to a legitimate doping control program). Also lending to its lack of popularity with non-tested athletes, is that it's somewhat obscure and (as a result) expensive.

Excerpt from Iron Magazine:
http://www.ironmagazine.com/2016/clostebol-explained/

Thoughts on Clostebol from T-Nation Forums:
https://forums.t-nation.com/t/thoughts-on-clostebol/136573

Clostebol:

It is the 4-chloro derivative of the natural hormone testosterone. The chlorination prevents conversion to dihydrotestosterone (DHT) while also rendering the chemical incapable of conversion to estrogen.

• A synthetic anabolic - androgenic steroid
• A weak AAS
• Has potential use as a performance enhancing drug
• It is currently banned by the World Anti-Doping Agency
• Clostebol acetate ointment has ophthalmological and dermatological use

Chlorodehydromethyltestosterone (Oral Turinabol), combining the chemical structures of clostebol and metandienone, was widely used in the East German state-sponsored doping program.

Use of clostebol has led to the suspension of a number of athletes in various sports including Freddy Galvis of the Philadelphia Phillies in 2012, Dee Gordon of the Miami Marlins in 2016, and Olympic athlete Viktoria Orsi Toth in 2016.