Over time, methylphenidate has proven to have high abuse liabilities.  In January of 2002, a study of rats and their sensitization to the reinforcing effects of cocaine after pretreatment with methylphenidate was published.  They found that following a 9 day exposure to cocaine, rats pretreated with methylphenidate acquired cocaine self administration much more quickly than those rats pretreated with a control saline solution.

The DEA states that it has been proven that neither animals nor humans can tell between cocaine and methylphenidate when administered in comparable doses.

Methylphenidate produces stimulus effects similar to cocaine.  Biologically, methylphenidate and cocaine have the same affinities for the dopamine transporter, however cocaine has a much higher affinity for the serotonin transporter, giving the feeling of euphoria not achieved by taking methylphenidate.
 
 

Schrenk, Susan and Sari Izenwasser.  "Pretreatment with methylphenidate sensitizes rats to the reinforcing effects of cocaine."  Pharmacology, Biochemistry, and Behavior, 72, 2002, 651-657.

Other Related Links:
 Kinetics of ritalin and cocaine