Boldenone undecylenate is an extremely versatile drug and, as such, combines very well with other steroids. An example of a great mass building stack would be 300-400mg/week of Boldenone undecylenate with 500mg of Sustanon or Testosterone Enthanate. For mass building purposes it can also be effectively stacked with Anadrol. This would result in significant gains in strength and mass without the additional side effects that would result from using the androgen alone. In terms of its use as part of a cutting cycle, Boldenone undecylenate combines very well with non-aromatizable steroids such as Trenbolone acetate or Winstrol. However, even the extremely low aromatization rate of these substances may be enough to cosine usage to bulking cycles only.
Boldenone undecylenate, or boldenone 17β-undec-10-enoate, is a synthetic androstane steroid and a derivative of testosterone .    It is the C17β undecylenate (undecenoate) ester of boldenone , which itself is δ 1 -testosterone, 1-dehydrotestosterone, or androsta-1,4-dien-17β-ol-3-one.    Boldenone is the non- 17α-alkylated variant of metandienone (17α-methyl-δ 1 -testosterone).    An AAS related to boldenone undecylenate is quinbolone (δ 1 -testosterone 17β-cyclopentenyl enol ether).  
ONC1-0013B inhibits AR activity in vitro. A. ONC1-0013B structure. B. LnCAP cells cultured (10% CSS) for 3 days, then treated with tested compounds in presence of 1nM DHT for 1 day. PSA expression plotted as percentage of vehicle control (DMSO; n=2, mean±SEM). Ki values: ± (ONC1-13B), ± (MDV3100), (ARN-509). Mean±SEM from 5 replicate experiments (except ARN-509). C. LnCAP cells cultured (10% CSS) for 3 days, then treated with tested compounds in presence of 1nM DHT for 5 days. Viable cells plotted as percentage of vehicle control (DMSO; n=2, mean±SEM). IC50 values: 30nM (ONC1-13B), 148nM (MDV3100), 240nM (ARN-509). D. Competitive-binding assay vs AR ligand Fluormone™ (PolarScreen™ Androgen Receptor Competitor Assay). IC50 values: 19nM (DHT), (ONC1-13B), (MDV3100).