From the FDA Drug Label
The maximum effect of daily doses of dutasteride on the reduction of DHT is dose dependent and is observed within 1 to 2 weeks. In patients with BPH treated with dutasteride 0.5 mg/day for 4 years, the median decrease in serum DHT was 94% at 1 year, 93% at 2 years, and 95% at both 3 and 4 years.
The FDA drug label does not answer the question of when to use a dihydrotestosterone (DHT) blocker with hormone replacement therapy (HRT). The provided information discusses the mechanism of action, pharmacodynamics, and pharmacokinetics of dutasteride and finasteride, but does not address the specific question of using DHT blockers with HRT.
From the Research
DHT blockers should be used in hormone replacement therapy (HRT) when there are concerns about male-pattern hair loss or when testosterone suppression alone isn't preventing androgenic effects, as evidenced by a study published in 2014 1. When considering the use of DHT blockers with HRT, it's essential to weigh the benefits and risks. The most common DHT blockers used are finasteride (typically 1-5mg daily) and dutasteride (0.5mg daily).
- Consider adding a DHT blocker if you're experiencing continued hair loss despite adequate testosterone suppression,
- if you have a family history of male pattern baldness,
- or if you started HRT after significant hair loss had already begun. These medications work by inhibiting the enzyme 5-alpha reductase, which converts testosterone to the more potent DHT. While estrogen and testosterone blockers reduce overall testosterone levels, some tissues remain sensitive to even small amounts of DHT, particularly hair follicles. Side effects may include reduced libido, erectile dysfunction (if pre-operative), and rarely, mood changes. DHT blockers are generally not necessary if you're not experiencing or concerned about hair loss, as standard HRT regimens with adequate testosterone suppression often provide sufficient results for most individuals. A study published in 2008 2 demonstrated that dutasteride reduces intraprostatic DHT levels by 83-93%, which can be beneficial in preventing prostate enlargement. However, the most recent and highest-quality study published in 2014 1 found that coadministration of finasteride with testosterone enanthate increased muscle strength and bone mineral density without causing prostate enlargement, suggesting that DHT blockers can be a useful addition to HRT regimens in certain cases. It's crucial to consult with a healthcare professional to determine the best course of treatment for individual cases.