Most of the studies done on the negative side effects of steroids are anecdotal and based on case reports -- no large retrospective or prospective studies have been conducted.
Here is a list of some of the known potential side effects of steroid use, compiled by the ABC News medical unit from interviews with medical specialists and information from the National Institute on Drug Abuse.
Masculinization This happens more frequently in females and is usually due to increased testosterone. The mostly irreversible side effects include increased facial hair, male-pattern baldness, increased acne, changes in skin texture, growth of facial and body hair, aggressiveness, and irritability.
Feminization Feminization occurs only in men and happens when excessive testosterone is converted to the female hormone estrogen. This results in the formation of breasts, decreased sperm count, decreased libido, shrunken testes, soft muscle mass and impotence. With drug treatment, side effects can be reversed.
Cardiovascular Steroids increase the cholesterol level in the body by increasing the "bad cholesterol," which can lead to clogs in the blood vessels -- leaving users susceptible to heart disease and strokes. In addition, steroids provoke a rapid increase in body weight and an accompanying rise in blood pressure, both of which leave users more vulnerable to a cardiovascular event. These side effects can be reversed to the extent if they are caught before the person has a heart attack or a stroke.
Growth Defects This is an important side effect to mention for high school athletes because steroids can cause the premature closure of the growth plate, leading to stunted growth.
Kidney Problems Toxic products like steroids put the kidneys under stress and can lead to electrolyte imbalances and high blood pressure. Kidney problems are reflected by lower back pain, increased swelling in the lower legs and ankles, and fever.
Liver Problems Based on estrogen studies in 1970s and 1980s, steroids could lead to certain tumors and liver damage.
Skin The skin is the largest organ of the human body and is the most sensitive organ to steroids -- especially in women. Pores grow large and acne problems that are not aided by typical over-the-counter medication can occur. Stretch marks also become prominent, though they are not directly caused by steroids. They stem from the rapid weight gain and muscle growth that steroids bring.
Neuropsychiatric Neuropsychiatric side effects are based mostly on case reports, but have been studied by two prominent Harvard psychiatrists, Drs. Harrison Pope and Kurt Brower from McLean Hospital in Belmont, Mass. Small studies indicate that long-term abuse can mimic bipolar disorder.
Symptoms will start off with a mania that leads to aggressiveness, reckless behavior and diminished need for sleep -- also known as "'roid rage." Some athletes could actually be seeking this last side effect, as it could lead to motivation to work out harder and a higher level of aggression when playing sports. It is almost always followed by a profound depression that can then lead to suicidal behavior.
There is a suspected psychologically addictive aspect to steroid use that leads athletes to become addicted to the way they feel on steroids and the way they look -- possibly leading to continued steroid abuse after their sport-playing days are over.