I've started researching test boosters, to make sure that my 40's go well, training wise. So far, the only supplement that has given me noticeable results is ZMA. It's not a test booster per se, but it puts you in REM sleep longer, and helps you sleep deeper. I'm a business owner, and I always have stuff waking me up in the middle of the night. Not anymore. My wife is taking it too, and we both agree, it's the best sleep we've ever had. Since I'm healing faster, there's almost no DOMS, my joints feel better, and I wake up feeling good. As hard as I'm training, there is less stress to my CNS. I have more energy.
I can't believe there's an over the counter product that actually works better than advertised. And it's cheap too, maybe $10 for a month.
Here are some studies done on it (
The anabolic effects of ZMA - Nutrition Express Articles). For the most part, it's positive data. Myself, I definitely noticed a difference after the first night, and my weights and reps are up. There's no placebo effect here. The quality of sleep has gone up so much, that I'd take this even if I wasn't training.