I can't find much clinical data on S4 Adarine, so this info put forth is from what I've gathered from reading various logs and reviews and my on personal experience.

S4 Andarine will increase stamina, strength, and is somewhat of a hardener, but you want put on much size unless stacked with something for mass gain. I've read it actually has anti estrogen properties. I've had blood work drawn while on ostarine and s4 and had low E2 basically crashed at 5.7. Someone else was using ostarine and did bloodwork and had crashed E2 as well, so we attributed low E2 to ostarine, but this is still up for debate, could have possibly been the S4. This could be the reasoning behind S4 giving you a dry hardened look. I liked stacking the ostarine and S4 together, I would compare it to about the same as a low dose testosterone 250 mg ew and 30 mg of anavar ed. Very good cutter, I was just doing maintenance diet and gained a few pounds.

S4 does come with a side effect for some, which I didn't experience. It can cause you to have a yellow tint in vision and blindness at night. For instance driving at night and somebody shines headlights and you start to get blind spots, so because and proceed with caution and ramp up doses to get a feel for S4, don't just jump to 50 mg out the gate.

Dosing protocol:
Start at 25 mg ed for a week or 2 and then bump to 50 mg anything higher you're increasing risk for yellow tint and night vision blindness.
It has a short half life so you could do 25 mg 2 hrs before gym time and 25 mg later. Somewhere I read stated it could be used just taking 50 mg 2 hrs before training 3 or 4 times a week.

I really liked S4 and it help keep my gains the later half of pct and off cycle and didn't experience any shut down.