Anabolic steroids are tiny molecules made of carbon atoms arranged in a ring. Their size and atomic composition allows them to easily enter cells and get into the brain of the cell, called the nucleus. There, they tell the cell to make different proteins by attaching to small molecules called receptors. 


When the anabolic steroid attaches, or binds to the receptor, the cell knows it’s time to change what proteins it’s making. Proteins aren’t just important in your diet to build muscle: all of your cells make protein, and they are essential for structure and function. Anabolic steroids change the amount of a type of proteins that are made. 


Anabolic steroids need to bind to receptors in skeletal muscle and in the muscles in our arms and legs that we use for lifting, to cause the changes in protein production.  In muscle cells, anabolic steroids enter the nucleus and change how much of certain proteins are made.

Proteins that are involved in building muscle are upregulated, meaning the steroids ‘up’ the number of them being made.  Proteins that are involved in breaking down muscle are downregulated, meaning less of them are made.