Boldenone (INN, BAN), (train name Equipoise) is a long-acting injectable anabolic agent for horses, supplied in a vial providing 50 mg boldenone undecylenate per mL in sesame oil with 3% (w/v) benzyl alcohol as a preservative. The activity of boldenone is mainly anabolic, with a low androgenic potency. Boldenone will increase nitrogen retention, protein synthesis increases appetite and stimulates the release of erythropoietin in the kidneys.

Boldenone was synthesized in an attempt to create a long-acting injectable methandrostenolone (Dianabol), for androgen deficiency disorders. Boldenone acts similar to methandrostenolone with fewer adverse androgenic effects. Although commonly compared to nandrolone, boldenone lacks progesterone receptor interaction and all the associated progestogenic side effects. Equipoise (Boldenone Undecylenate Injection) is recommended as an aid for treating debilitated horses when an improvement in weight, haircoat or general physical condition is desired. Debilitation often follows disease or may occur following overwork and overexertion. Boldenone improves the general state of debilitated horses, thus aiding in correcting weight losses and improving appetite. It is not a substitute for a well-balanced diet. Optimal results can be expected only when good management and feeding practices are utilized. Boldenone should be considered only as adjunctive therapy to other specific and supportive therapy for diseases, surgical cases, and traumatic injuries.

Boldenone:
https://drugs.ncats.io/drug/5H7I2IP58X

Equipoise was the very first synthetic derivative compound of testosterone ever produced - created years before Dianabol was created. Equipoise was created in 1949, it wouldn't be until the early 1960s and that it really started to take off as a performance-enhancing drug. Between 1949 in the 1960s, the chemists behind this solution played with the combination of esters that had been attached to the main chemicals in this compound - and that's what led them to extending the release time as well as the overall half-life of this steroid. A number of clinical trials were unveiled in the 1960's to see if this primarily veterinary only drug could be used safely on humans, and bodybuilders throughout the 1960's, 1970's, and 1980's jumped on board before those clinical trials ever finish up.

In the 1970's, researchers found that there were a number of other anabolic steroids better at helping to prevent muscle wasting and weight loss problems - two of the medical reasons Equipoise was supposed to be prescribed to individual patients - and eventually it was removed from the market. Even still, bodybuilders and athletes these early days of this drug continued to use it on a regular basis. When it was discontinued in the 1970's a pharmaceutical company called Squibb decided to pick up the patents for this drug compound. They rebranded Equipoise as Boldenone, offered it to veterinarians and horse owners/breeders and enjoyed a tremendous amount of success with this switch. Over the next few decades the patents and formula for Equipoise have changed hands a dozen times or more, but every time the formula has remained the same - and continues to produce lean muscle mass production increases unlike almost anything else out there while also bringing effective appetite stimulant effects to the table as well.

Excerpt from steroidabuse.org:
https://www.steroidabuse.org/steroid-profiles/equipoise-boldenone-undecylenate/

Boldenone itself has never been marketed as a pharmaceutical drug - it is used as boldenone undecylenate, the undecylenate ester:
https://en.wikipedia.org/wiki/Boldenone

Boldenone undecylenate:

• Boldenone Undecylenate is a synthetic androgen and anabolic steroid
• Introduced for medical use in the 1960s
• Used in veterinary medicine mainly in horses
• It was formerly used in humans but was discontinued
• It is given by injection into muscle
• Strong anabolic effects
• Moderate androgenic effects
• Weak estrogenic effects
• Has no risk of liver damage
• Half-life of 14 days when administered by intramuscular injection.
• Side effects of boldenone undecylenate include symptoms of masculinization like acne, increased hair growth, voice changes, and increased sexual desire

Boldenone was reportedly patented by Ciba in 1949, and esters of the compound were developed by the company in the 1950s and 1960s. One such ester, boldenone undecylenate, was introduced for clinical use as an injectable AAS under the brand name Parenabol in the 1960s. However, it was discontinued for use in humans in the late 1970s. Squibb introduced boldenone undecylenate for veterinary use under the brand name Equipoise. The medication has been used much more widely in veterinary medicine, in which it has been used mainly in horses, and remains in use today.