Cytomel is not a steroid, but more a of a cutting aid. It’s a synthetic form of the thyroid hormone tri-iodio-thyronine or T3, made up of a metabolite of the amino acid tyrosine and 3 iodine ions. In the body it in turn is made from another hormone, T4, which is secreted by the thyroid under influence of the pituitary hormone TSH (Thyroid stimulating hormone). If a shortage of either TSH or T4 is noted, usually doctors may opt for a replacement therapy. These days the most common prescription is synthetic T4 (synthroid), but in more severe cases of permanent thyroid dysfunction, the choice is given to Cytomel. Simply because T4 is mostly active through its conversion to T3 and T3 is 4-5 times stronger than T4 on a mcg for mcg basis. In bodybuilding circles Cytomel is mostly used as fat-loss drug. Thyroid hormones are often referred to as the metabolic regulators of the body. High levels of T3 speed up the metabolism of an individual, allowing him to burn more calories and use calories more sufficiently. Generally ectopmorphic body-types have very high thyroid levels and in some cases a slight undiagnosed form of hyperthyroidism. Both hyper-and hypothyroidism can have severe consequences on an individual, such as goiters and other nasty stuff, so messing with your thyroid is not something I would advise to beginners. As with insulin, misuse of this compound can leave you dependent on exogenous T3 for the rest of your life (remember Frank Zane?). So some caution and research is required before putting Cytomel in your body. Generally cycles should be limited to 4-6 weeks tops, I recommend 3 and alternating cycles with 3-week cycles of clenbuterol. But most importantly, to avoid a crash or a shock to the thyroid function doses need to be built up over time and tapered off again. More so for cytomel than for any other drug in existence.