The short answer: Many patients report feeling much better in 2-4 weeks, and full affects are felt after the first month
Understanding testosterone half-life
Half-life is the point at which medication in the body is reduced by 50%. Testosterone has a half-life of 8-days.
There is a misconception that half-life works like this:
The reality is much better and works like this:
As you can see, the medication levels are slowly reduced. However, during this time patients take continued doses, which looks like this:
As you can see, it takes time for the results to compound.
NOTE: The chart above is for representational purposes, and assumes once-weekly shots. Patients taking twice-weekly shots, or topical testosterone daily, would have a chart pattern with smaller and more frequent changes.