Finasteride is not an anabolic steroid, but its chemical structure is technically steroid-based. It belongs to a class called 4-azasteroids, meaning it has a modified steroid backbone with a nitrogen atom swapped into the ring structure. This modification changes its behavior entirely. Instead of building muscle or boosting hormones like anabolic steroids do, finasteride blocks the conversion of testosterone into a more potent hormone called DHT.
This distinction matters because the word “steroid” carries a lot of baggage. Understanding what finasteride actually does, and what it doesn’t do, clears up the confusion.
What “Steroid” Means in Finasteride’s Case
In chemistry, “steroid” refers to a specific molecular shape: four interconnected carbon rings. Cholesterol has this shape. So do cortisol, estrogen, testosterone, and vitamin D precursors. Having a steroid structure doesn’t make something an anabolic steroid any more than having wheels makes a shopping cart a race car. The shape is just a starting framework.
The National Cancer Institute classifies finasteride as a “synthetic 4-azasteroid compound.” Its full chemical name, (5alpha,17beta)-N-(1,1-dimethylethyl)-3-oxo-4-azaandrost-1-ene-17-carboxamide, reveals that it’s built on an androstane skeleton (the same backbone as testosterone) but with a nitrogen atom replacing one of the carbon atoms in the A-ring. That single substitution completely changes how the molecule behaves in your body. It can no longer activate androgen receptors the way testosterone or DHT would. Instead, it parks itself in an enzyme and shuts it down.
How Finasteride Actually Works
Your body converts a portion of its testosterone into dihydrotestosterone (DHT) using an enzyme called 5-alpha reductase. DHT is significantly more potent than testosterone at stimulating the prostate and hair follicles. Finasteride blocks the type II version of this enzyme, preventing that conversion from happening.
The effect on DHT levels is substantial. A 1 mg daily dose (the standard for hair loss) reduces DHT in scalp tissue by roughly 64% and in the bloodstream by about 71%. The 5 mg dose used for prostate enlargement pushes those numbers slightly higher, to around 69% in scalp tissue and 72% in the blood. This is the opposite of what anabolic steroids do. Anabolic steroids flood the body with androgens; finasteride removes one of the most potent androgens from circulation.
Interestingly, finasteride causes a modest increase in total testosterone. Because less testosterone is being converted to DHT, more of it stays in its original form. This increase is real but small, and it’s most noticeable in men who had low testosterone levels to begin with. It’s nowhere near the kind of spike you’d see from taking exogenous testosterone.
How It Differs From Anabolic Steroids
Anabolic steroids work by directly activating androgen receptors in muscle, bone, and other tissues, triggering protein synthesis and tissue growth. They cause measurable increases in muscle mass, strength, and body composition. Finasteride does none of this. It has no direct anabolic activity.
A revealing study in older men with low testosterone looked at what happens when you combine testosterone therapy with finasteride. The testosterone increased upper and lower body muscle strength by 8 to 14%, added about 4 kilograms of fat-free mass, and improved bone mineral density. Adding finasteride to the regimen didn’t change any of those muscle or bone benefits. What finasteride did block was the testosterone-induced prostate enlargement, which grew by 11.4 cubic centimeters with testosterone alone but didn’t change when finasteride was added.
This tells us something important: the muscle-building effects of testosterone come from testosterone itself acting on androgen receptors, not from its conversion to DHT. Finasteride strips away the DHT-driven effects (prostate growth, scalp oil production, hair follicle miniaturization) without touching the anabolic ones. That’s why it’s sometimes combined with testosterone therapy in clinical settings, to get the benefits while limiting prostate-related risks.
What Finasteride Is Prescribed For
Finasteride has two FDA-approved uses. At 1 mg daily, it treats androgenetic alopecia (male pattern hair loss) by reducing the DHT that causes hair follicles to shrink over time. At 5 mg daily, it treats benign prostatic hyperplasia (BPH), the non-cancerous prostate enlargement that can make urination difficult in older men. Both conditions are driven by DHT activity in specific tissues, and both respond to lowering DHT levels.
Side Effects to Be Aware Of
Because finasteride alters hormone levels, it can affect sexual function in some men. Clinical trials have reported sexual side effects in roughly 2% to 4% of users. Erectile difficulties are the most common complaint, followed by changes in ejaculation and reduced libido. In long-term studies, the rate of these side effects dropped below 2% and was comparable to what men taking a placebo reported.
A systematic review of twelve randomized trials covering nearly 4,000 men found about double the risk of erectile dysfunction compared to placebo. However, the number of men who actually stopped taking the drug because of sexual side effects was no different from the placebo group, suggesting the effects are mild enough for most men to continue treatment. Some reports describe persistent sexual side effects after stopping the drug, though this remains a topic of active clinical debate and the incidence is unclear.
Why the Confusion Exists
The confusion around finasteride and steroids comes from a few places. Its chemical name contains “androst,” which sounds like “androgen.” It modifies hormone levels. It shows up in conversations about testosterone and DHT. And the word “steroid” in its classification (4-azasteroid) triggers alarm bells for anyone who associates steroids with performance-enhancing drugs.
But pharmacologically, finasteride is an enzyme inhibitor. It doesn’t add hormones to your body, doesn’t activate androgen receptors, and doesn’t promote muscle growth. It reduces one specific hormone by blocking the enzyme that creates it. That puts it in a fundamentally different category from anabolic steroids, even though they share a distant chemical ancestry.