I'm opposite, primo makes my hair thin and Mast doesn't. I have both but only an open mast e right now, only thing I could think would be different is that Mast is a very thin compound, thin like cyp vs enanthate. I can get mast and cyp into my biceps with a 25g zero pip, enan I need to use a 23g 1.5" to get it deep enough in a glute, 400mg/ml gives me a lump for a day. But everyone is different, I volunteer you and I to decipher this with 1 shot from each vial, we'll get to the bottom of this, hell, I won't even charge.