Pharmacogenetics of Finasteride

Finasteride is a medication that is commonly used to treat male pattern baldness, also known as androgenetic alopecia. It works by inhibiting the conversion of testosterone into dihydrotestosterone (DHT), which is a hormone that contributes to hair loss in men. Here are some key points about finasteride in hair loss treatment:

How Finasteride Works:

  • DHT Reduction: Finasteride blocks the action of an enzyme called 5-alpha reductase, which converts testosterone into DHT.
  • Hair Follicle Protection: By reducing DHT levels, it helps to protect hair follicles from the damaging effects of DHT, allowing them to continue producing hair.


  • Hair Growth: Clinical studies have shown that finasteride can promote hair regrowth and slow down hair loss in men with male pattern baldness.
  • Crown vs. Hairline: It is generally more effective at regrowing hair at the crown (top) of the head than at the hairline.


  • Daily Pill: Typically, it is taken as a once-daily oral tablet.
  • Long-Term Use: To maintain results, it’s usually necessary to continue taking finasteride indefinitely.


  • Side Effects: Some men may experience side effects such as decreased libido, erectile dysfunction, or reduced ejaculate volume. These usually go away if the medication is stopped.
  • Pregnancy: Finasteride can cause birth defects if taken by a woman during pregnancy, so it’s important to avoid handling broken or crushed tablets if pregnant.

Who Should Use It:

  • Men: Finasteride is approved for use in men only.
  • Pattern Baldness: It’s most effective for men with male pattern baldness.
  • Consultation: It’s recommended to consult with a healthcare provider before starting finasteride to discuss its potential benefits and risks.


  • Timeframe: It may take several months to a year to see noticeable effects on hair growth.
  • Maintenance: Continued use is necessary to maintain the benefits.


Finasteride is a medication primarily used to treat male pattern baldness (androgenetic alopecia). Like any medication, it can have side effects. For the treatment of hair loss, finasteride is usually taken in a lower dose (1mg) compared to its use for prostate issues. Here are some common side effects of finasteride used for hair loss:

Common Side Effects:

1. Sexual Side Effects:

  • Erectile dysfunction
  • Decreased sexual desire
  • Problems with ejaculation (such as decreased volume of ejaculate)

2. Breast Tenderness or Enlargement:

  • Some men may experience breast tenderness or enlargement (gynecomastia).

3. Skin Rash:

  • Some individuals might develop a rash or itching.

4. Other Less Common Side Effects:

  • Swelling in the hands or feet
  • Dizziness
  • Weakness
  • Headache
  • Runny nose

Serious Side Effects (Rare):

1. Allergic Reactions:

  • Difficulty breathing
  • Swelling of the face, lips, tongue, or throat
  • Severe itching or skin rash

2. Depression:

  • Some individuals may experience changes in mood, including depression or anxiety.

3. Testicular Pain:

  • Pain or discomfort in the testicles is a rare side effect.

4. Male Breast Cancer:

  • There have been reports of male breast cancer in men taking finasteride, though this is extremely rare.


It’s important to remember that not everyone will experience these side effects, and some individuals may have no side effects at all. If you notice any concerning side effects, it’s crucial to contact your healthcare provider. The sexual side effects are the most commonly reported and can sometimes persist even after stopping the medication. This is a rare but known phenomenon called Post-Finasteride Syndrome (PFS).

Post-Finasteride Syndrome (PFS):

PFS is a controversial topic in medicine, with some patients reporting persistent sexual, neurological, and physical side effects after discontinuing finasteride. The medical community is still studying this condition to better understand its causes and treatment. If you are experiencing side effects from finasteride, it’s important to speak with your healthcare provider. They can provide guidance on whether to continue the medication, adjust the dosage, or explore alternative treatments for hair loss.

Pharmacodynamics of Finasteride:

Finasteride works by inhibiting the enzyme 5-alpha reductase, which converts testosterone to dihydrotestosterone (DHT). DHT is implicated in the miniaturization of hair follicles seen in androgenetic alopecia.

Genetic Variations:

  • CYP3A4 and CYP3A5: These genes code for enzymes involved in the metabolism of finasteride. Variations in these genes can affect how quickly or slowly an individual metabolizes the drug.
  • SRD5A2: This gene codes for the 5-alpha reductase enzyme that finasteride inhibits. Variations in this gene could influence the effectiveness of finasteride treatment.
  • Androgen Receptor (AR) Gene: Variations in the AR gene can influence the sensitivity of hair follicles to DHT, which could impact the effectiveness of finasteride.

Studies and Findings:

  • Research has indicated that variations in the CYP3A4 gene may affect the metabolism of finasteride, potentially impacting its efficacy.
  • A study published in the Journal of the American Academy of Dermatology in 2019 found that variations in the CYP3A4 and CYP3A5 genes influenced the efficacy of finasteride treatment for androgenetic alopecia. Individuals with certain genetic variants had a better response to finasteride.

Clinical Considerations:

Pharmacogenetic testing is not yet a standard practice for prescribing finasteride for hair loss. However, as our understanding of personalized medicine grows, it could become more relevant. Currently, finasteride is generally prescribed based on standard dosages, with adjustments made based on individual response and side effects.

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