GP Mast 100 by Geneza Pharmaceuticals is an injectable steroid which contains the hormone Drostanolone Propionate. Geneza Pharmaceuticals offers Drostanolone in two different preperations, 100mg per ML as Drostanolone Propionate and 200mg per ML as Drostanolone Enanthate/Drostanolopne Propionate blend. Masteron, as it is often called, is most commonly used by bodybuilders who are in the "cutting" phase of their training and dieting. While only mildly anabolic, this steroid extremely androgenic and because of this, brings about a very pronounced amount of hardness and definition to the muscles. On top of this, GP Mast 100 is also noted as being an effective estrogen blocker, and also binds to SHBG, making it possible for other steroids being used to bind more easily to their respective receptors, thus making their presence in the body much more effective. These effects are also noted by bodybuilders who choose to use the oral preparation of Masteron, Proviron. Bodybuilders looking to incorporate GP Mast 100 into a cycle might stack it with other steroids such as Trenbolones, Testosterone propionate, and oral compounds such as Stanozolole or Halotestin to bring about an even more pronounced amount of definition and hardness leading up to a contest. Common androgenic side effects are possible with Masteron, such as oily skin and increased libido. Due to its extremely androgenic properties, this drug is not a favorite among women bodybuilders, although most serious competitors still choose to use it due to its effectiveness as a pre-contest drug. Males typically use a dosage of this steroid ranging from 300-600mgs per week while women typically prefer a dosage range of 100-300mgs per week. This drug is often injected once every 2-3 days to help maintain consistent blood levels.
PXR is activated by a large number of endogenous and exogenous chemicals including steroids (., progesterone , 17α-hydroxyprogesterone , 17α-hydroxypregnenolone , 5α-dihydroprogesterone , 5β-dihydroprogesterone , allopregnanolone , corticosterone , cyproterone acetate , spironolactone , dexamethasone , mifepristone ), antibiotics (., rifampicin , rifaximin ), antimycotics , bile acids , hyperforin (a constituent of the herbal antidepressant St. John's Wort ), and many herbal and other compounds (. meclizine , paclitaxel ).  Cafestol found in coffee is also an agonist. 
This is my second time using this particular Lab. I've previous positive experience with Sis (when formerly known as Infiniti Labs) Anavar, so my expectations were some what inflated:)
Firstly, I was really impressed by the immaculate packaging of this product, which shows how much effort went into its manufacturing and marketing. I ran this product at a weekly dose of 400mg, in conjunction with Mast e and Test. Prior to introducing Sis Tren e into my current cycle, I was already using a different Labs Tren at a slightly higher dose of 500mg weekly. To be honest, I did not notice any difference, even when running Sis Tren e at a slightly lowered dose of 400mg for 5 weeks in total. I continued with making strength gains with a noticeable reduction in body fat, even though my diet wasn't always on point. I have had no adverse effects from the Tren, unless if you want to include night sweats. Overall, I am very satisfied with the results I got from use of this product.