I had a very short run with TRT a little over a year ago and can offer a little feedback based on the experience. I had started with a TT level of 330ng/dl and was prescribed 1 tube of Testim (I think 5g) daily. 2 weeks later I was retested at 120ng/dl. The exogenous test caused shutdown rapidly (LH dropped to basically zero as well) and the replacement test/amount I absorbed wasn't enough to have me break even. In my case, it looked like complete shutdown occurred pretty fast and endogenous test wouldn't be a factor in future TT readings if I had continued.