The following is a post I received from a friend who is a clinician at 
UC Berkely.
Note the citation....
YA> VOLKOW et. al.  1995.  IS METHYLPHENIDATE LIKE COCAINE?  
YA> Studies on Their Pharmacokinetics and Distribution in the 
YA> Human Brain.  Archives of General Psychiatry. 52:456-463
YA> 
YA> This paper provides a nice comparison of methylphenidate and 
YA> cocaine.  The first sentence states, "Cocaine which is one 
YA> of the most reinforcing and addictive of the abused drugs, 
YA> has pharmacological actions that are very similar to those 
YA> of methylphenidate hydrochloride..."  It's noted that 
YA> "cocaine and methylphenidate substitute for each other on 
YA> discriminative experiments..."
YA> 
YA> The authors indicate that cocaine and methylphenidate have 
YA> similar affinities for the dopamine transporter.  This is 
YA> interesting because cocaine's addictiveness is related to 
YA> it's ability to inhibit the dopamine transporter.  But 
YA> methylphenidate doesn't have the same addiction profile as 
YA> cocaine.  While humans will repeatedly self-administer 
YA> cocaine, they do so much less frequently with 
YA> methylphenidate.  
YA> 
YA> The authors inject radiolabeled cocaine or methylphenidate 
YA> into humans and baboons and take PET scans of their brains.  
YA> They ask the the humans to rate on a scale of 0-10 how high 
YA> they are (0 is sober, 10 is stoned-out-of-your-mind).  Then 
YA> they see if there is a corellation between the subjective 
YA> stonyness rating and the drug activity noted on the scans.
YA> 
YA> From the scans it's found that methylphenidate and cocaine 
YA> take a similar amount of time to reach peak concentration in 
YA> the brain, but the cocaine stays at peak levels for less 
YA> than 5 minutes, while methylphenidate stays at peak levels 
YA> for up to 20 minutes..
YA> 
YA> Now combining this data with the subjective stonyness 
YA> ratings reveals that the high is correlated to the *change* 
YA> in drug concentration.  So the faster the dopamine levels 
YA> change in the synapse, the better the high.  
YA> 
YA> To simplify this, when you take cocaine you shoot your 
YA> dopamine levels up from 0-10.  40 minutes later you are back 
YA> down to around 4.  You can take more cocaine and knock your 
YA> dopamine back up to 10 (a change of 6).
YA> 
YA> With methylphenidate you shoot up from 0 to 10, but then 
YA> after 40 minutes, your dopamine is still at 8 or 9.  If you 
YA> take more you can restore levels to 10, but this is only a 
YA> change of 1 or 2.  Remember, it's the rate of increase, the 
YA> change in dopamine levels that causes the high.
YA> 
YA> So you are both right.  Ritalin and Cocaine are very 
YA> similar.  They also have some differences that turn out to 
YA> be significant when it comes to addiction and abuse.
So, Jane, see, there is a difference!
 * RM 1.31  * Eval Day 15 * Closed mouths accept no feet.
--- Platinum Xpress/Wildcat! v1.3
---------------