Short answer: The Propecia Patient Information says that if you forget to take Propecia, do not take an extra tablet. Just take the next tablet as usual. Propecia is one 1 mg tablet a day, and the label says it takes 3 months or more of daily use to see a benefit, so one missed day changes little.
| Situation | What the label says |
|---|---|
| Schedule | One 1 mg tablet once daily, with or without food (2) |
| Forgot a tablet | Do not take an extra one; take the next as usual (Patient Information) |
| Time to see a benefit | 3 months or more of daily use (2) |
| If stopped | Effect reverses within 12 months (2) |
| Half-life | About 5 to 6 hours in men 18 to 60 (12.3) |
The Patient Information says: if you forget to take Propecia, do not take an extra tablet. Just take the next tablet as usual.
Example: you take finasteride every morning and realize the next morning that you missed yesterday. Under the label you would take one tablet today, not two.
Section 2 says daily use for three months or more is generally needed before a benefit shows, and continued use keeps it. The effect builds over months, so one missed tablet does not undo it. The finasteride half-life is about 5 to 6 hours in men 18 to 60 (section 12.3), but the label is built around steady daily use, not each dose.
Section 2 says that if treatment stops, the effect reverses within 12 months. The label does not give a restart rule; talk to your prescriber after a long gap.
This page summarizes FDA labeling. It is not personalized medical advice; confirm what to do with your prescriber or pharmacist.