u/77poprocks

Is it possible with a 5/16 needle that it's not going deep enough? I've been struggling with trimix for awhile now, made it up to 40 units with a 5/16 needle with the needle all the way in and the erections didn't last and weren't fully hard, last night I tried 5 units, but I pushed the needle to where the tip of the syringe was buried in my penis, ended getting 50% erection with no stimulation, after about 45 minutes my wife decided she wanted to get intimate with me and that got me to 75-85% erection and it lasted over 2 hours. Have I just been doing this wrong all along? Should I step up to a 1/2 needle? I'm average girth, so I figured 5/16 was plenty