While 8 weeks will be our minimal time frame, 12 weeks is far more efficient, with 16 weeks being the gold standard. Absolutely, you can run cycles that extend past the 16 week mark, but the only ones who will typically have a need for this will be advanced competitive bodybuilders . In any case, for the sake of your health you will need to plan off-cycle periods. You need to allow time periods where there is not a high influx of hormones so as to allow your body to normalize and relieve it from stress. Failure to do this can really mess with your natural hormone production, and in many cases lead to you lifelong hormone therapy needs.