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.
Anabolic processes tend toward "building up" organs and tissues . These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules . Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass. Endocrinologists have traditionally classified hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The classic anabolic hormones are the anabolic steroids , which stimulate protein synthesis, muscle growth, and insulin .  The balance between anabolism and catabolism is also regulated by circadian rhythms , with processes such as glucose metabolism fluctuating to match an animal's normal periods of activity throughout the day.