Anabolic steroids are usualy abused by athletes to improve performance. the following is a copy and paste job from 'wikipedia'Body composition and strength improvements
A review spanning more than three decades of experimental studies in men found that body weight may increase by 2–5 kg as a result of short term (<10 weeks) AAS use, which may be attributed mainly to an increase of lean mass. Animal studies also found that fat mass was reduced, but most studies in humans failed to elucidate significant fat mass decrements. The effects on lean body mass have been shown to be dose dependent. Both muscle hypertrophy and the formation of new muscle fibers have been observed. The hydration of lean mass remains unaffected by AAS use, although small increments of blood volume cannot be ruled out.[31]
The upper region of the body (thorax, neck, shoulders and upper arm) seems to be more susceptible for AAS than other body regions because of predominance of androgen receptors in the upper body. The largest difference in muscle fibre size between AAS users and non-users was observed in type I muscle fibres of the vastus lateralis and the trapezius muscle as a result of long-term AAS self-administration. After drug withdrawal the effects fade away slowly, but may persist for more than 6–12 weeks after cessation of AAS use.[31]
The same review observed strength improvements in the range of 5-20% of baseline strength, largely depending on the drugs and dose used as well as the administration period. Overall, the exercise where the most significant improvements were observed was the bench press.[32] For almost two decades it was assumed that AAS only exerted significant effects in experienced strength athletes, particularly based on the studies of Hervey and coworkers.[33][34] In 1996 a randomized controlled trial published in the New England Journal of Medicine demonstrated however that even in novice athletes a 10-week strength training program accompanied by testosterone enanthate at 600 mg/week may improve strength more than training alone does.[32][35] The same study found that dose was sufficient to significantly improve lean muscle mass relative to placebo even in subjects that did not exercise at all.[35] A 2001 study by the same first author, showed that the anabolic effects of testosterone enanthate were highly dose dependent.[31][36]
Adverse effects
Psychiatric effects
A 2005 review in CNS Drugs determined that "significant psychiatric symptoms including aggression and violence, mania, and less frequently psychosis and suicide have been associated with steroidabuse.
Aggression and hypomania
From the mid-1980s onwards the popular press has been reporting "roid rage" as a side effect of AAS (the term being a play on the more established phenomenon of road rage).[66]
A 2005 review determined that some, but not all, randomized controlled studies have found that anabolic steroid use correlates with hypomania and increased aggressiveness, but pointed out that attempts to determine whether AAS use triggers violent behaviour have failed, primarily because of high rates of non-participation.[67] A 2008 study on a nationally representative sample of young adult males in the United States found an association between lifetime and past-year self-reported anabolic-androgenic steroid use and involvement in violent acts. Compared with individuals who did not use steroids, young adult males who used anabolic-androgenic steroids reported greater involvement in violent behaviors even after controlling for the effects of key demographic variables, previous violent behavior, and polydrug use.[68] A 1996 review examining the blind studies available at that time also found that these had demonstrated a link between aggression and steroid use, but pointed out that with estimates of over one million past or current steroid users in the United States at that time, an extremely small percentage of those using steroids appear to have experienced mental disturbance severe enough to result in clinical treatments or medical case reports.[69