Finasteride DHT and PSA Effects: 1 mg vs 5 mg

Clinically grounded: Values are group averages from the FDA prescribing information and a published dose-ranging study (Drake 1999). Individual variation exists. Reviewed by our medical team. Not a substitute for medical advice.

Finasteride blocks 5-alpha reductase type II, the enzyme that converts testosterone to dihydrotestosterone (DHT). The table below shows how much DHT fell, on average, in the studies behind each dose. These are group results from study participants, not a prediction for any one person.

Understanding the numbers

Measure	Finasteride 1 mg/day	Finasteride 5 mg/day	Study details
Serum DHT	71.4% lower	72.2% lower	Drake 1999: 249 men with male pattern hair loss, 42 days
Scalp DHT	64.1% lower	69.4% lower	Drake 1999: scalp biopsies before and after 42 days
Serum DHT (label)	65% lower within 24 hours of a dose	About 70% lower with daily use for up to 4 years	Propecia and Proscar US prescribing information
Prostate tissue DHT	About 80% lower in men with BPH given 1 to 100 mg/day for 7 to 10 days before prostate surgery		Proscar US prescribing information
PSA	Mean 0.7 to 0.5 ng/mL at 12 months (men aged 18 to 41)	About 50% lower in older men with BPH	Propecia and Proscar US prescribing information

Group averages from the cited sources. Placebo also lowered scalp DHT by 13.0% in Drake 1999.

The difference between 1 mg and 5 mg in serum DHT suppression is small (71.4% vs 72.2% in Drake 1999). The same study found that doses as low as 0.2 mg per day already produced the maximal fall in scalp and serum DHT. The 5 mg dose is the one approved for BPH, where prostate size is the target.

PSA and finasteride: what you must know

PSA note: Finasteride lowers PSA test results, so tell whoever orders your PSA test that you take it. For finasteride 5 mg (Proscar) taken for six months or more, the label advises doubling an isolated PSA value before comparing it with normal ranges for untreated men, and setting a new PSA baseline at least six months after starting treatment. The Propecia (1 mg) label gives no doubling rule; it reports a fall from 0.7 to 0.5 ng/mL in men aged 18 to 41. With either dose, any confirmed rise from your lowest PSA value on treatment should be checked by a doctor, even if it is within the normal range.

Frequently asked questions

Can I use these numbers to predict my own DHT or PSA?

No. They are averages from groups of study participants, and individual responses vary. A PSA result taken while on finasteride should be interpreted by the clinician who ordered it, using the rules in the prescribing information described above.

Why is scalp DHT reduction different from serum?

The scalp’s sebaceous glands and hair follicles contain their own 5-alpha reductase activity. In a dose-ranging study with scalp biopsies (Drake 1999), 1 mg lowered serum DHT by 71.4% and scalp DHT by 64.1% after 42 days. Topical finasteride formulations target this compartment more directly.

Does a higher DHT reduction mean better hair results?

Not necessarily. The 1 mg vs 5 mg difference in scalp DHT is small (64.1% vs 69.4% in Drake 1999), and the same study found maximal scalp DHT reduction at doses as low as 0.2 mg per day. For male pattern hair loss, 1 mg is the FDA-approved dose.

How long does it take to reach full DHT suppression?

Quickly. The Propecia label reports 65% serum DHT suppression within 24 hours of a 1 mg dose. In the Proscar label, DHT returned to pretreatment levels about 2 weeks after healthy volunteers stopped a 14-day course. Visible hair changes take much longer; see the results timeline.

Sources: Drake L, et al. The effects of finasteride on scalp skin and serum androgen levels in men with androgenetic alopecia. J Am Acad Dermatol. 1999;41(4):550-4. PROPECIA (finasteride) tablets, US Prescribing Information. PROSCAR (finasteride) tablets, US Prescribing Information.