Inhibits the conversion of testosterone to dihydrotesterone by the enzyme 5alpha-reductase, thereby reducing the most active androgen in the prostate by 90 %.

Finasteride, which is an irreversible inhibitor of 5α-reductase but only inhibits the type II and III isoenzymes: dutasteride is able to achieve a reduction in circulating DHT levels of up to 98%, whereas finasteride is able to achieve a reduction of only 65 to 70%.

In spite of the differential reduction in circulating DHT levels, the two drugs decrease levels of DHT to a similar extent of approximately 85 to 90% in the prostate gland, where the type II isoform of 5α-reductase predominates.

Proscar and Propecia trade names.

Shrinks the prostate by 20-30 % and improves urinary flow and symptoms in benign prostatic hyperplasia.

Reduces BPH associated hematuria.

Adverse effects include decreased libido, ejaculation dysfunction and gynecomastia.

Decreases PSA levels by 50% and can lead to false negative results while monitoring for prostate cancer.

Decreases the need for surgical treatment in BPH from 10 to 5 %.

Reduces the prevalence of biopsy confirmed prostate cancer in patients treated for 7 years by 24.8% over placebo.

Finasteride slightly decreases body mass, particularly among men who have low testosterone levels before starting treatment.

While incidence of prostate cancer is lower with the use of finasteride compared to placebo the likelihood of having a Gleason’s grade 7-10 tumor is increased.

The 5-ARI finasteride reduces the prostate cancer risk by about a third.

5-ARIs may increase the fraction of aggressive forms of prostate cancer. 

Finasteride inhibits the function of two of the isoenzymes (types 2 and 3) of 5α-reductase.

Prostate Cancer Prevention Trial (PCPT) showed a 25% relative risk reduction in the incidence of prostate cancer with the use of finasteride in the study that included more than 8000 and then was a randomized placebo control study.

Finasteride improves detection of prostate cancer in high-grade prostate cancer by improving the performance characteristics of PSA test, digital rectal exam and the prostate biopsy.

Prostate Cancer Prevention Trial (PCPT)the use of finasteride was associated with a 6.4% diagnosis of high grade prostate cancer as opposed to 5.1% in the placebo arm.

In the above study the 25% lower risk of death from prostate cancer with finasteride was not statistically significant.

In the above trial, at 7 years, the use of finasteride reduced the risk of a prostate cancer being diagnosed, but did not affect mortality.

Prostate Cancer Prevention Trial (PCPT) Indicated finasteride reduced the risk of prostate cancer by about one third and high-grade prostate cancer was more common in the treatment group than in the placebo group, but after 18 years therevwas no significant difference in the groups in overall survival, or survival after the diagnosis of prostate cancer (Thompson IM et al).

Associated with sexual adverse events including erectile dysfunction, that may persist even after stopping this agent.

Associated with male infertility and poor semen quality, that improves after discontinuation of the medication.

May reduce libido during and after use, it may be associated with ejaculation disorders and orgasm disorders.

Can be used in male-pattern hair loss.

In a study of 89 women with hyperandrogenism due to persistent adrenarche syndrome, finasteride produced a 93% reduction in facial hirsutism and a 73% reduction in bodily hirsutism after 2 years of treatment.

Other studies using finasteride for hirsutism have also found it to be clearly effective.

Finasteride is not indicated for women and is not recommended in pregnant women.

Finasteride is effective starting within 6 weeks of treatment, and causes an increase in hair retention, the weight of hair, and some increase in regrowth.

It decreases circulating DHT levels by up to about 70%.

Side effects in about 2% of males, include decreased sex drive, erectile dysfunction, and ejaculatory dysfunction.

It has a short terminal half-life of only 5 to 8 hours.

Finasteride has also been associated with intraoperative floppy iris syndrome and cataract formation, depressive symptoms and suicidality have been reported.

Finasteride and dutasteride are  associated with a significantly increased risk of depression and self-harm during the first 18 months of treatment, but were not associated with an increased risk of suicide.

However, it has  a warning of increased risk of suicide.

Treatment should be continued as long as positive results occur.

Once treatment is stopped, hair loss resumes.

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