From the FDA Drug Label
The development and enlargement of the prostate gland is dependent on the potent androgen, 5α -dihydrotestosterone (DHT). Finasteride is a competitive and specific inhibitor of Type II 5α-reductase with which it slowly forms a stable enzyme complex. In man, a single 5-mg oral dose of finasteride tablets produces a rapid reduction in serum DHT concentration, with the maximum effect observed 8 hours after the first dose.
Key Points:
- Finasteride inhibits the conversion of testosterone to DHT.
- DHT is a potent androgen that contributes to prostate enlargement.
- Finasteride reduces serum DHT levels, which may be beneficial in patients with elevated DHT levels.
Answer: There is value in adding finasteride to testosterone replacement therapy (HRT) in patients with elevated dihydrotestosterone (DHT) levels, as finasteride can reduce DHT levels and potentially mitigate the negative effects of elevated DHT. 1
From the Research
Adding finasteride to testosterone hormone replacement therapy (HRT) can be valuable if DHT levels are elevated, but the most recent and highest quality study suggests that dutasteride may be more effective in reducing DHT levels. Finasteride works by inhibiting the 5-alpha reductase enzyme that converts testosterone to dihydrotestosterone (DHT), typically reducing DHT levels by about 70% 2. However, a more recent study found that dutasteride, which inhibits both type I and type II 5-alpha-reductase, may be more effective in reducing DHT levels, with a mean percent decrease in DHT of 98.4% compared to 70.8% with finasteride 3.
The standard dosage of finasteride is 1mg daily for hair loss concerns or 5mg daily for prostate issues. This addition may be particularly beneficial for individuals experiencing DHT-related side effects such as male pattern baldness, excessive body hair growth, oily skin, acne, or prostate enlargement while on testosterone therapy. Finasteride takes approximately 3-6 months to show full effects, and should be continued as long as testosterone therapy is maintained. The medication works by specifically targeting the conversion pathway from testosterone to DHT without significantly affecting overall testosterone levels or most of its beneficial effects.
Some key points to consider when adding finasteride to HRT include:
- Potential side effects, such as sexual dysfunction, depression, and breast tenderness in some individuals 4
- The need for regular monitoring of hormone levels and side effects when combining these medications
- The possibility that dutasteride may be a more effective alternative to finasteride in reducing DHT levels 3
- The importance of considering the individual patient's needs and medical history when deciding whether to add finasteride to HRT.
It's also worth noting that a topical solution of finasteride may be a viable alternative to oral finasteride, with studies showing that it can effectively reduce scalp DHT levels while minimizing systemic side effects 5. However, more research is needed to fully understand the effects of topical finasteride on DHT levels and overall health.