“Deals don't keep hours.” That's what we said at the firm, half joke, half badge. Nobody complained about the short nights, so I didn't either.

By nine I could barely keep my eyes open at my desk. By eleven, lights off, I was wide awake: tomorrow's meeting, today's mistake, no way to turn it down.

Then the rest of me started to slip. My workouts stopped paying off. Same sessions in the gym, less to show for them, and less in the tank every week.

My drive went too. For work, for training, for everything. I couldn't hold my focus through a meeting, and the 3 o'clock coffee became the 3 and the 5 o'clock coffee.

I snapped at people over details that didn't matter and forgot the ones that did. The people who knew me best stopped asking if I was okay.

One late-night search turned into the whole sleep section on PubMed. I expected to read about sleep. I kept reading about testosterone.

It's the hormone behind a man's drive, muscle, stamina, energy and focus. And your body makes most of it at night, in deep sleep.

In a University of Chicago study, healthy young men slept five hours a night for one week. Their daytime testosterone fell by 10–15%. That's about what ten years of ageing takes. They felt it too: less energy, lower mood.

My days didn't end at six. They ended when the deal did, and nobody had told my body the day was over.

I was exhausted and wired at the same time. Asleep on the sofa at nine. Wide awake in bed at eleven.

With cortisol that high, you don't drop into deep sleep. And deep sleep is when your body makes testosterone. Eight hours in bed like that isn't eight hours of rest.

No deep sleep. Less testosterone. Less drive, less strength, less energy, less focus. Night after night, for two years.

This is not a testosterone booster. There's no testosterone in it, and it won't push your levels above what's natural for you.

What it does is turn the stress off at night, so you get the deep sleep where your body makes its own.

If what you want is to be knocked out, buy a sleeping pill. This won't do that either. And two capsules don't fix a bad week. They stop a bad week turning into a bad month.

It took me 2 years to build Sleep & Recovery, with neuroscientists, athletes and the people who actually make this stuff. We had one rule: every ingredient at the dose the research used, or it doesn't go in.