For anyone who has reviewed the downstream mechanisms of Finasteride in the body, it is clear that this is not true.
Below are the details to a realistic set of expectations from Finasteride use with anabolic steroids.
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Not All Steroids Convert to DHT via 5-Alpha Reductase
An assumption that must be ruled out is the idea that dihydrotestosterone (DHT) will always be the by-product of metabolic reactions between 5-alpha reductase and an anabolic steroid.
5-alpha reductase is an enzyme involved in steroid metabolism that can create androgenic metabolites (e.g. DHT) via a process called “5-alpha reduction”.
While several studies indeed support the idea that DHT is an influencer for hair-loss and that anabolic steroids all have a certain tendency to interact with 5-alpha reductase, most of the steroids used for bodybuilding and powerlifting are not potent substrates for 5-alpha reductase, if they interact at all.
Testosterone is the only anabolic steroid that is converted to DHT via 5-alpha reductase, which is contrary to the common misconception that all other anabolic steroids would also be converted to DHT.
Other steroids that are substrates for 5-alpha reductase are converted to unique metabolites with their own individual anabolic and androgenic potency.
For example, Boldenone (Equipoise) can be converted to dihydroboldenone (DHB) via 5-alpha reductase.
Nandrolone can be converted to dihydronandrolone (DHN) via 5-alpha reductase.
The two metabolites DHB and DHN each have their own unique anabolic and androgenic potency and will not be equal to one another, nor will they be equal to DHT.
Testosterone vs. Other Anabolic Steroids as a Catalyst for Hair Loss
Excessive intake of testosterone can definitely result in an increased susceptibility to hair loss due to its interaction with 5-alpha reductase to produce DHT, as well as via its inherent anabolic activity, albeit to a much lesser extent.
Meanwhile, certain synthetic anabolic steroids such as Primobolan are designed to maximize the anabolic activity in the body with a lower incidence of androgenic activity and do not interact with 5-alpha reductase at all.
However, just because a steroid does not interact with 5-alpha reductase that does not mean that the parent hormone is hair safe whatsoever.
There are several other steroids that do not interact with 5-alpha reductase that will still cause hair loss.
The overarching concept that needs to be remembered is that all steroids have their own individual level of anabolism and androgenicity in tissues.
Regardless if a steroid is a 5-alpha reduced metabolite, or a parent hormone, they are all still steroids at the end of the day with their own anabolic and androgenic impact on affected tissues in the body, and they need to all be accounted for.
Anabolic Steroid Interaction With 5-Alpha Reductase
Finasteride is essentially a downstream androgen synthesis inhibitor.
This particular medication reduces the formation of the potent androgen, dihydrotestosterone (DHT), from its precursor testosterone by successfully inhibiting the 5-alpha reductase enzyme.
Since DHT is several times more androgenic than testosterone, this would significantly decrease the amount of androgenic influence on the body.
An important aspect to take into consideration is that the parent hormones themselves are inherently androgenic to a significant extent.
In fact, with some steroids, the metabolites could be far less androgenic than the parent hormone, in which case 5-alpha reduction could actually be more hair loss sparing.
Nandrolone is an example of this, where the parent hormone (nandrolone) is more androgenic than its metabolite produced via 5-alpha reduction (DHN); subsequently making concurrent Finasteride use an accelerant of androgenic alopecia.
Finasteride Only Prevents DHT Derived Hair Loss
To sum up, Finasteride may meaningfully prevent hair loss only if the cause is due to excess DHT.
This is because DHT is more several times more androgenic than testosterone.
DHT exhibits such poor anabolic tissue selectivity that it is one of the few steroids that actually features an androgenic rating several times higher than its anabolic rating.
In short, DHT sucks at building muscle.
In a study conducted to determine whether the intake of Dutasteride would affect muscle mass accrual, those treated with the medication had similar results to the untreated control group; meaning that the decreased DHT level had no significant anabolic impact on muscle growth.
In fact, an argument can be made that inhibiting 5-alpha reductase can mediate supraphysiological muscle growth due to a higher ratio of testosterone to DHT.
This is apparent in pseudohermaphrodites who are inherently 5-alpha reductase-deficient due to genetic mutations [R].
In this particular study involving brothers with different DHT levels, the male with 5-alpha reductase deficiency experienced reduced sexual development throughout puberty, but also gained more muscle mass than his brother.
In the image below, the man on the left has a 5-alpha reductase deficiency, and his brother on the right doesn't have a deficiency.
The man on the left has a higher testosterone level, is more muscular, and has less androgenic alopecia than his brother on the right who has normal DHT levels.
The Steroids Finasteride Or Dutasteride Can Protect Your Hair From
Finasteride and Dutasteride do not occupy or inhibit androgen receptors, but rather they inhibit the 5-alpha reductase enzyme primarily responsible for converting testosterone to DHT.
These medications are extremely effective at reducing DHT levels, hence why natural athletes and those on mild doses of exogenous testosterone typically experience the attenuation of hair loss progression with it, or at least some degree of slow down (dependent on the individual's androgen receptor density, sensitivity, residual DHT levels, free testosterone levels, and a myriad of other less relevant factors).
Those who blast Trenbolone, or any other anabolic steroid, will not be protected from the androgenic activity of those hormones on the scalp.
It is essential to thoroughly understand the mechanism of action of everything going into your body prior to haphazardly popping pills in attempts to blindly remedy a side effect like hair loss, as you may be wasting your time, or even potentially make the situation worse.