There is a risk of contamination the more you handle it. That said, a lot of people make their own blends from various vials. I have done it a bunch of times. I have made a blend recently that is Test 100 mg/mL, Primo 75 mg/mL, nandrolone 33 mg/mL. It's 208 mg/mL total and convenient to do injects EOD that way.