Finasteride is a medication prescribed to address conditions such as male pattern hair loss (androgenic alopecia) and benign prostatic hyperplasia (BPH), an enlarged prostate gland. This article clarifies how the body processes and eliminates finasteride, and how long it remains in the system.
How the Body Processes Finasteride
Finasteride is well absorbed into the bloodstream after oral intake, with about 65% bioavailability; food does not affect its absorption. Peak blood concentrations occur within one to two hours. The drug undergoes extensive metabolism, primarily in the liver, through the cytochrome P450 enzyme system, specifically the CYP3A4 enzyme. It converts finasteride into metabolites that are less than 20% as active as the original compound.
Finasteride and its metabolites are eliminated primarily through feces (57-64%) and urine (39-40%). The half-life, the time for half the drug to be eliminated, ranges from 5 to 6 hours for finasteride, though this can vary from 3 to 16 hours. A substance is generally cleared from the body after four to five half-lives.
Factors Influencing Elimination
Several individual factors can influence how long finasteride remains in a person’s system. Age is a factor; in men over 70, the half-life of finasteride can be prolonged to eight hours or more. This extended half-life means it takes longer for the drug to clear in older individuals.
Liver function also plays a role, as finasteride is extensively metabolized in the liver. Impaired liver function can slow this metabolic process, leading to a longer presence of the drug. Specific dose adjustments for hepatic impairment are not typically provided, though caution is advised. Kidney function does not usually necessitate dose adjustments, as the body can compensate by increasing fecal excretion if renal elimination is reduced.
When Finasteride is No Longer Active
When finasteride is discontinued, its concentration decreases, leading to the cessation of its therapeutic effects. Finasteride primarily reduces dihydrotestosterone (DHT) levels, a hormone involved in male pattern hair loss and prostate enlargement. Serum DHT levels return to pre-treatment levels within about 14 days after stopping the medication.
After DHT levels return to baseline, the treated conditions may reappear. For male pattern hair loss, hair shedding can resume, and any hair growth gains may diminish over several months to a year. For benign prostatic hyperplasia, prostate volume may return to its original size within about three months, potentially leading to a return of associated symptoms. Side effects, such as sexual dysfunction, commonly resolve within days, weeks, or months after the drug is eliminated.