Finasteride is a medication prescribed for male pattern hair loss and benign prostatic hyperplasia (enlarged prostate). It reduces dihydrotestosterone (DHT), a hormone contributing to hair thinning and prostate growth. Understanding how finasteride is processed and eliminated clarifies its overall presence and effects.
How Finasteride Leaves Your System
Once finasteride is ingested, it is readily absorbed into the bloodstream. The liver processes the drug through metabolic pathways, transforming it into compounds that can be more easily eliminated.
Finasteride’s half-life is approximately 5 to 7 hours. This indicates the time it takes for the concentration of the medication in the body to decrease by half. After roughly four to five half-lives, most of the drug is considered to be cleared from the system.
For finasteride, this generally means that the medication is almost entirely eliminated from the bloodstream within 3 to 5 days for most individuals. Factors such as a person’s age or the efficiency of their liver function can influence this clearance rate. Older individuals or those with impaired liver function might experience a slightly prolonged elimination time.
How Long Finasteride Affects DHT Levels
Finasteride inhibits the enzyme 5-alpha-reductase. This enzyme is responsible for converting testosterone into dihydrotestosterone (DHT), the hormone that finasteride aims to reduce. The inhibition of this enzyme begins shortly after the drug is absorbed and continues as long as a sufficient concentration of finasteride is present in the body.
Even after finasteride clears the bloodstream, its suppressive effect on 5-alpha-reductase and DHT levels can persist. This is because the enzyme’s activity is suppressed, and it takes time for the body to produce new, active enzyme. Therefore, DHT levels in the scalp and prostate may remain suppressed for several weeks, often up to a month, after the last dose of the medication.
This prolonged biological effect means finasteride’s therapeutic benefits, such as reduced hair loss or prostate shrinkage, do not immediately cease upon discontinuation. The body gradually restores its baseline DHT levels over this extended period. This distinction between the drug’s physical clearance and its lasting biological impact is important for understanding its overall influence.
What Happens When You Stop Taking Finasteride
When finasteride is discontinued, the inhibition of the 5-alpha-reductase enzyme gradually diminishes. As the enzyme’s activity recovers, the body’s natural production of dihydrotestosterone (DHT) will begin to increase. This leads to DHT levels slowly returning to what they were before treatment began.
For male pattern hair loss, the return of DHT to pre-treatment levels typically means hair loss progression will resume. The hair follicles that were previously protected from DHT’s effects will once again become susceptible to its influence. This often results in the gradual thinning and loss of hair observed prior to starting the medication.
The timeframe for hair loss resumption can vary among individuals but is commonly observed within 3 to 12 months after stopping finasteride. The exact timing depends on how quickly DHT levels rebound and the inherent susceptibility of hair follicles to DHT. Consistent use is generally needed to maintain its hair-preserving effects.