High dosages of oral corticosteroids taken daily for prolonged periods of time can have serious systemic side effects including bone loss ( osteoporosis), increased risk of infections and diabetes and cataracts, thinning of skin, stretch marks, increased facial/body hair growth, acne, fluid retention, weight gain with redistribution of fat (fat deposits on back and face, thinning of limbs), muscle weakness, decreased resistance to infections, stomach ulcers, mood swings, insomnia, suppression of the body's own production of cortisol, etc.
Cartman's plan of course fails, having failed to consider that the handicapped contestants all had months of intensive training and are in great shape while he was not. He comes in last in the Special Olympics. However, he gets a spirit award in the form of a gift voucher to Shakey's Pizza. When he comes up to the stand to collect the prize, Jimmy realizes Cartman has been faking his "retardation" and ironically is about to beat him up for being a cheater, but Timmy scolds him for it. Jimmy learns his lesson, namely that taking steroids is cheating, on a par with pretending to be "retarded" in order to participate in the Special Olympics. This results in him giving back his medal and delivering a heartfelt speech to the audience, who applaud him for being honest.
There was some controversy surrounding "Up the Down Steroid" and the 2005 film The Ringer , as both feature the same plot: someone pretending to be disabled in order to compete in the Special Olympics.  The Ringer was written and filmed months before this episode was aired, although, The Ringer was not released to the public until after this episode aired. According to the episode's DVD audio commentary, series co-creators Trey Parker and Matt Stone did not think that they ripped off The Ringer , since the idea to them did not seem hard to come up with, and they did not even think it was big enough for a twenty-minute episode let alone a two-hour film.  In the opening scene, the boys are playing the same "Investigative Reports with Bill Kurtis " funtime game as they did in the season four episode " Cartman Joins NAMBLA ".