I'm not sure what causes it but there are three natural boosters that I use that all work wonders for me. One's not made anymore (I stocked up) called "Pink Magic" by USP labs. Second is also by USP labs, "PRIME" and the third is "Beast SuperTest" by Beast Sports Nutrition. I have tried everything, from DAA to Tribulus, etc. Nothing but these three ever showed me signs of something similar to testosterone increases. Do they actually raise your test levels? Dunno. But they do, 1. Drive you sexually and makes your stuff work like when you were young 2. Leans out and hardens the muscles. 3. Just increases your overall masculine feelings, deepens your voice, etc. So if its not increasing test, its doing something thats' simulating that. Either way these three really work for me.