There is widespread evidence that the use of testosterone and other anabolic steroids may result in irreversible changes in physiology and the body's chemistry. In addition, anabolic steroids have been linked to a number of health conditions. These include liver tumors, cancer, high blood pressure, increases in bad cholesterol (LDL), and kidney tumors. Anabolic steroids also have significant effects on certain groups of people. In men, shrinking of the testicles, reduced sperm count, infertility, baldness, development of breasts, and increased risk for prostate cancer have been reported. In women, growth of facial hair, male-pattern baldness, menstrual irregularity, enlargement of the clitoris and a deepened voice have been reported. In children, prematurely halted growth has been reported.

The regular use of anabolic steroids often results in extreme psychiatric side effects. Regular users may experience extreme irritability, delusions, paranoia, unabated jealousy, and impaired judgment stemming from feelings of invincibility. In this way, the user poses a significant risk to not only him or her self, but also to the friends, family, and community who may encounter the addict in such a state.

Individuals who share needles to inject steroids may be at risk for sharing and/or spreading serious diseases, including hepatitis C and HIV/AIDS.

Individuals who purchase smuggled, homemade, or illegally obtained steroids take the significant risk of purchasing tainted products, which could result in serious illness, injury, or death.

Most prohormones have not been thoroughly studied, and the long-term effects of their use are not known.

The Food and Drug Administration (FDA) has censured some herbal companies for selling anabolic steroids as dietary supplements. Consumers should be aware of these products, as they carry the same high risk for adverse effects as illegally taken steroids.

Anabolic steroids work in two ways simultaneously. First, the steroids increase the synthesis of testosterone in the body while simultaneously blocking the receptor that inactivates the hormones. Secondly, anabolic steroids block the effects of cortisol, a stress hormone, on muscle tissue. As a result, individuals who take anabolic steroids experience a variety of effects. The body's muscle mass and strength increases at an abnormally high rate. The rate of protein synthesis is elevated. Bone remodeling and growth occur much faster than before. Bone marrow is stimulated to produce more red blood cells.

Until the passage of the Anabolic Steroids Act of 2004, many athletes used prohormones (which were legal then) as an alternative to anabolic steroids. The precursors to actual hormones, prohormones caused similar, although less drastic results as taking steroids. Prohormones are now classified as a controlled substance, and are illegal for the purpose of athletic performance enhancement.

The human body goes through five steps to produce hormones. The ingestion or injection of prohormones skips at least one of these five steps, and thus increases the body's production of testosterone.

Although clinical studies have shown the effectiveness of anabolic steroids for certain medical conditions and testosterone enhancement, the number of potential side effects is quite large. Regardless of the efficacy of this practice, the use of anabolic steroids for a use other than that prescribed to a patient is illegal in the United States.

Testosterone and anabolic steroids are taken orally, or they may be self-injected. Often, athletes take multiple anabolic steroids simultaneously, according to one of two methods, cycling or stacking. Both of these methods are considered equally dangerous.

Cycling: Athletes take multiple types of high dose steroids simultaneously in cycles of weeks or months, and then abstain from their use for a wash out period before beginning the cycle again. This pattern is thought to maximize the benefits of the steroids by preventing the body from adjusting to, and thus weakening the effects of the drugs.

Stacking: Individuals take multiple brands or types of anabolic steroids simultaneously in the belief that such a dosing pattern will have more of an effect than any one drug taken individually. While this pattern is thought to reduce the short-time side effects of anabolic steroid abuse, it does not in any way minimize the often irreversible long-term side effects.

Some individuals turn to other drugs to counteract the immediate side effects of steroids (e.g. irritability or acne). Such use may result in further medical complications or multiple addictions.

It is illegal to bring anabolic steroids, including testosterone, into the United States with the intent to use the drugs to boost athletic performance or to distribute to athletes.