Are prohormones any different from steroids?

Short answer

No. A prohormone that did build muscle cut good cholesterol by 38.7% and raised a liver enzyme by 113.8% in 4 weeks. Older prohormones that built no muscle still raised estrogen and lowered good cholesterol.

Are prohormones any different from steroids?
'Just a raw material → mild and safe' — does this formula hold?
Prohormones are substances the body converts into hormones such as testosterone. They were sold as supplements with the claim that, being a 'raw material' rather than a steroid, they are mild. We checked what was actually different.
Older prohormones did not raise testosterone
No extra muscle or strength over 8 weeks
20 people did 8 weeks of strength training while taking androstenedione or a fake pill. Testosterone levels did not change, and gains in strength and muscle did not differ from the fake pill. Instead, estrogen (estradiol) rose from 220 to 280 to 310.
Instead, the body's balance was thrown off
Good cholesterol and the body's own testosterone fell
In the same study, good cholesterol (HDL) fell from 42 to 37 within 2 weeks. In another trial where 50 people took it for 12 weeks, testosterone rose 16% after 1 month, then returned to where it started by week 12. That was because the body's signal to make its own testosterone dropped by 18 to 33%.
Newer prohormones were different
Muscle grew in 4 weeks
After the US banned 18 ingredients, including androstenedione, in 2004, 17 people tested a newer prohormone for 4 weeks. Lean mass (muscle and everything except fat) rose 6.3%, more than with a fake pill (0.5%), and their heaviest squat rose 14.3%, more than with the fake pill (5.7%).
Once it worked, side effects followed
Good cholesterol down 38.7% in 4 weeks
In the same trial, those on the prohormone saw good cholesterol drop 38.7% and bad cholesterol (LDL) rise 32.8% in 4 weeks. A liver enzyme (AST) rose 113.8%, and the kidneys' ability to filter blood fell 18.0%. Nothing changed in the fake pill group.
The labels could not be trusted
Steroids turned up in 14 products
44 people whose livers were damaged by bodybuilding supplements all developed jaundice, and 71% were hospitalized. Of the 33 products they took, 14 contained steroids, mostly different from what the label listed. An analysis of 634 supplements from 13 countries found steroids in about 15% of non-hormone products.
Summary: the prohormone that built muscle was a steroid
The formula breaks at the 'mild' link
Older prohormones built no muscle and only worsened estrogen and cholesterol. The newer prohormone that did build muscle left good cholesterol down 38.7% and a liver enzyme up 113.8% in 4 weeks. When it worked, it came with the same costs as steroids.