Slang for insulin and typically used by bodybuilders.
Insulin is a highly anabolic hormone; however, it is not a steroid. A steroid is a type of hormone, but not all hormones are a steroid. Insulin is not a steroid because it not a
derivative of a lipid; however, other than that, it is very similar to a steroid. For this reason testing for insulin is non existent.
Insulin by itself will not give you big muscles, it is best used with
anabolic steroids that increase
muscle tissue, such as
Testosterone, Deca, and Dianabol. This is known as "stacking hormones".
The reason insulin is a great muscle builder is because of one simple fact: Every cell stores glycogen. Excess calories you eat will be converted into glycogen. Insulin tells every single cell in your body (muscle, fat, connective, even nervous tissue cells) to store glycogen. When you inject insulin you're essentially forcing your cells to take in more glycogen.
This is where the stacking comes in. Using insulin without steroid hormones your body will give all the glycogen to your fact cells, making you fatter. This is why insulin has a bad rep for weight gain. Steroid hormones (especially the 3 I listed) make your muscles bigger, allowing a higher quantity of glycogen to be stored in your muscles. Steroids also block fat
production, meaning glycogen won't go to the fat cells. The combination of all this causes insulin to be very powerful in terms of building muscle size.