How Does Finasteride Work? Mechanism of Action & Metabolic Effects
Learn how Finasteride 1mg tablets treat male pattern hair loss by inhibiting 5-alpha-reductase and reducing DHT levels in the scalp.
Key Takeaways
- Mechanism: Finasteride is a competitive inhibitor of Type II 5α-reductase
- Target: Specifically blocks conversion of testosterone to dihydrotestosterone (DHT)
- Effect: Reduces scalp DHT by approximately 60% with 1mg daily dose
- Result: Reverses miniaturization of hair follicles in androgen-sensitive areas
- Timeframe: Noticeable results typically appear after 3-6 months of continuous use
Finasteride 1mg tablets contain the active substance finasteride, which is a synthetic 4-azasteroid compound that works by specifically targeting the enzymatic process that converts testosterone to dihydrotestosterone (DHT).
Chemical Composition of Finasteride Tablets
Finasteride 1mg tablets contain the active substance finasteride, which is a synthetic 4-azasteroid compound. Chemically, it is known as N-(1,1-dimethylethyl)-3-oxo-4-aza-5α-androst-1-ene-17β-carboxamide.
The molecular formula of finasteride is C23H36N2O2 with a molecular weight of 372.55 g/mol. The tablets also contain several inactive ingredients:
| Component | Function | Amount |
|---|---|---|
| Finasteride | Active ingredient | 1 mg |
| Lactose monohydrate | Filler/Binder | q.s. |
| Microcrystalline cellulose | Binder/Diluent | q.s. |
| Pregelatinised starch | Disintegrant | q.s. |
| Sodium starch glycolate | Superdisintegrant | q.s. |
| Lauryl macrogolglycerides | Surfactant | q.s. |
| Magnesium stearate | Lubricant | q.s. |
Mechanism of Action: How Finasteride Works
Finasteride belongs to a class of medications called 5-alpha-reductase inhibitors. Its mechanism of action involves specifically targeting the enzymatic process that converts testosterone to dihydrotestosterone (DHT).
The Testosterone to DHT Conversion
In the body, testosterone is converted to the more potent androgen DHT by the enzyme 5-alpha-reductase. There are two main isoforms of this enzyme:
- Type I: Predominantly found in sebaceous glands and the liver
- Type II: Primarily located in hair follicles, prostate gland, and liver
Finasteride is a competitive inhibitor of the Type II 5α-reductase isoenzyme. It binds to the enzyme's active site, preventing the conversion of testosterone to DHT.
DHT's Role in Hair Loss
DHT is a primary contributor to male pattern hair loss (androgenetic alopecia) through several mechanisms:
- Shortening of the anagen (growth) phase of the hair cycle
- Miniaturization of hair follicles
- Progressive transformation of terminal hairs into vellus hairs
By reducing DHT levels in the scalp by approximately 60%, Finasteride helps reverse these processes, allowing follicles to regain normal size and function.
Metabolic Effects and Pharmacokinetics
After oral administration, Finasteride is well absorbed with an average bioavailability of approximately 65%. Food intake does not significantly affect its absorption.
Distribution and Metabolism
Finasteride is extensively bound to plasma proteins (approximately 90%) and has a volume of distribution of 76 liters. It crosses the blood-brain barrier to a limited extent but is not known to significantly affect central nervous system function.
The drug is metabolized primarily in the liver via the cytochrome P450 3A4 enzyme system. Its two main metabolites are:
- ω-hydroxy finasteride (active but less potent than parent compound)
- Finasteride carboxylic acid (inactive)
Elimination
Finasteride has an elimination half-life of approximately 6-8 hours in men aged 18-60 years. It is excreted in both urine (39%) and feces (57%) as metabolites. Only minimal amounts of unchanged drug are excreted.
The reduction in serum DHT concentration is dose-dependent and maintained throughout the treatment period. With the 1mg daily dose used for hair loss, serum DHT levels are reduced by approximately 70%, while scalp DHT is reduced by about 60-70%.
Clinical Efficacy and Timeframe
Male pattern hair loss develops gradually over time, and the response to Finasteride treatment follows a similar pattern. Clinical studies have demonstrated:
- Increase in hair count visible after 3 months of treatment
- Significant improvement in hair growth after 6-12 months
- Further improvement observed with continued treatment for up to 2 years
- Maintenance of benefits with ongoing therapy
Continued use of Finasteride is necessary to maintain beneficial effects. If treatment is stopped, hair loss typically returns to pretreatment levels within 9-12 months.
Frequently Asked Questions
How quickly does Finasteride start working?
Finasteride begins working immediately to inhibit 5-alpha-reductase, but visible results take time. Most men notice initial improvements after 3-6 months of daily use, with more significant results appearing after 12 months. Maximum benefits are typically seen after 2 years of continuous treatment.
Does Finasteride affect testosterone levels?
Finasteride does not lower testosterone levels. By inhibiting the conversion of testosterone to DHT, it may actually cause a small increase in serum testosterone levels (typically 10-15%). However, this increase generally remains within the normal physiological range.
Can Finasteride cause permanent side effects?
While most side effects of Finasteride resolve after discontinuation, some men have reported persistent sexual side effects that continue after stopping the medication. This condition, known as Post-Finasteride Syndrome (PFS), is rare and not fully understood. The majority of users experience side effects that resolve within weeks to months after discontinuation.
How does Finasteride differ from Minoxidil?
Finasteride and Minoxidil work through completely different mechanisms. Finasteride is a systemic treatment that reduces DHT production throughout the body, addressing the hormonal cause of hair loss. Minoxidil is a topical treatment that works primarily as a vasodilator, improving blood flow to hair follicles and potentially prolonging the growth phase. The two medications are often used together for enhanced results.
Is Finasteride effective for all types of hair loss?
No, Finasteride is specifically effective for male pattern hair loss (androgenetic alopecia), which is DHT-dependent. It is not effective for other forms of hair loss such as alopecia areata, telogen effluvium, scarring alopecias, or hair loss due to nutritional deficiencies. Proper diagnosis by a healthcare professional is essential before starting treatment.
Considering Finasteride for Hair Loss?
If you're experiencing male pattern hair loss, our UK-registered doctors can help determine if Finasteride is appropriate for your condition through a confidential online consultation.
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Medical Content Manager
Nabeel is a co-founder and medical content manager of Chemist Doctor. He works closely with our medical team to ensure the information is accurate and up-to-date.
Medical Doctor
Dr. Feroz is a GMC-registered doctor and a medical reviewer at Chemist Doctor. He oversees acute condition and urgent care guidance.
Medical Director
Usman is a co-founder and medical director of Chemist Doctor. He leads the organisation's strategic vision, bridging clinical and operational priorities.
Review Date: 27 October 2025
Next Review: 30 April 2026
Published on: 27 October 2025
Last Updated: 28 October 2025
