Toxicology and carcinogenesis studies of methylphenidate hydrochloride
, a drug used in the treatment of attention-deficient disorders, were
performed in F344 rats and B6C3F1 mice. In these studies, methylphenid
ate hydrochloride was administered for 2 years at doses of 0, 100, 500
or 1000 ppm in the feed to rats and at doses of 0, 50, 250, 500 ppm t
o mice in groups that consisted of 50 animals/dose/sex/species. The av
erage amount of methylphenidate consumed per day was estimated to be 4
-47 mg/kg/day for rats and 5-67 mg/kg/day for mice. Survival was simil
ar in dosed and control groups. An increase in benign tumors of the li
ver and increased liver weights were observed in male and female mice
at the high dose. An increase in hepatoblastomas was also seen in high
dose male mice. Methylphenidate was not mutagenic in the Salmonella a
ssay system, and it is hypothesized that this tumorigenic effect might
be due to nongenotoxic effects of the chemical such as an increase in
cell proliferation. Increased incidences of neoplasms were not seen i
n rats. However, there was a notable decrease in mammary gland fibroad
enomas in female rats and a marginal decrease in benign pheochromocyto
mas in male rats. Epidemiology studies of methylphenidate have found n
o evidence of a carcinogenic effect in humans and like our findings in
rats, report a less than expected rate of cancers in patients taking
methylphenidate.