MAMMOTH P is a stable and organically-derived natural product. Unopened, MAMMOTH P will remain effective for two years after the manufacture date. Once opened, we recommend using your MAMMOTH P within one year for best results. The manufacture date can be found in the bottom right hand corner of the back side of the bottle. From left to right the numbers indicate the day, month, and year in which the bottle was manufactured, followed by the lot number of the bottle.