There are pregnenolone cream. And in some case of adrenal burnout with DHEA deficiency it might help. But really, pregnenolone can be converted to many many hormones:
- Estrogen (estriol, estradiol, estrone)
So simply elevating pregnenolone would not be enough to increase testosterone production. If you increase pregnenolone it simply gives the body more raw material but it can use that raw material to produce any of the hormones above.
As for testosterone, pregnenolone converts via...
Pregnenolone --) 17 hydroxypregnenolone --) DHEA --) Androstenedione --) Testosterone
We know that androstenedione is converted to testosterone at a rate of about 5% (so 100mg of andro would yield about a 5mg increase in testo). The further down the chain you do, the less direct increase in T you will have.
Let's say that you want to elevate T by taking pregnenolone. In reality you might increase estrogen, cortisol or aldosterone