Ritalin is typically used on a daily basis with a hiatus on weekends or during the summer. Because it is ingested almost daily for a period of years, there are major concerns over chronic health effects. The National Toxicology Program accepted responsibility for conducting trials on carcinogenicity and in June 1993 released results showing that feeding mice Ritalin induced liver tumors including very rare and highly malignant cancers. These results were found at levels close to those routinely prescribed for children. More studies are being planned for testing Ritalin, but the evidence is strong.
Animal tests are very good predictors of human health effects.
The response of the FDA and Ciba-Geigy to the cancer test results were not adequately protective of child's health. Animal tests are very reliable predictors of human effects. Of the 23 known human carcinogens, all were identified as carcinogens in animals first, sometimes decades earlier. It is disconcerting that the FDA is not making a move to ban or limit the use of this drug. While Ritalin is the most commonly used drug for attention deficit disorders, now prescribed to 60 to 90 percent of American children with such disorders, there are Pharmacological alternatives.