This is an important question and the answer to this question is of concern to many people. Cocaine and MP are very similar in both structure and route of action. When two drugs are very similar to one another a process called cross-sensitization can occur.
Q. What is cross-sensitization?
A. Cross-sensitization is an enhanced reactivity to a new drug caused by previous exposure to a drug that is similar to the new drug. An enhanced reactivity means that a person will respond to the new drug quicker and be more likely to feel the effects of that drug compared to a person for whom cross-sensitization has not occurred.
The major concern is that individuals who use MP in order to treat their ADD/ADHD, or abuse it recreationally, will become more responsive to the effects of cocaine and therefore become addicted to cocaine more easily. This is a difficult thing to test. In studies, cocaine users have reported the "high," they felt from MP (administered intravenously) as similar to cocaine. In addition cocaine users have reported MP administrations increased their cravings for cocaine.
Animal tests have been performed (Brandon et. al. 2001) to determine if methylphenidate treatment, in rats, causes an enhanced reactivity and vulnerability to cocaine. These tests have shown that rats treated with stimulants such as MP do indeed develop a decreased latency to cocaine self-administration. In these tests two groups of rats were used:
Group 1: Control Group, treated with a placebo (saline solution)
Group 2: Experimental Group, treated with MP
The rats were treated with their respective drugs for 7 days and then were not treated with anything for 2 weeks.
At the end of the 2 weeks the rats were put into a test chamber where they were implanted with a IV line which was attached to a mechanical syringe that would give the rats an injection of a low does of cocaine. The rats were trained that they could receive an injection by pressing a button in their test chamber.
The results of this study are shown in the following graph:
This graph shows that the rats that were treated with MP (solid black dots) administered themselves with cocaine significantly more times then rats that were treated with the saline solution. These results suggest that the MP did sensitize the rats to the effects of cocaine, which resulted in the MP rats actively trying to receive their cocaine injections more frequently.
(chart from: Brandon et. al. 2001)
The same study then attempted to determine if treatment with MP during adolescence would cause sensitization to cocaine in adults rats which had been treated with MP as adolescents.
5-week-old rats (adolescent) were treated with MP for a week.
The rats then went untreated until 8 weeks of age (adulthood).
At 8 weeks they were placed into the test chamber.
The experimenters observed the rat's "ambulations" and "rears," as a result of the cocaine administration.
Ambulations and rears are behaviors that rats exhibit in response to a particular stimuli. These behaviors can be interpreted to show how much of an effect of a drug an animal is feeling. Ambulations and rears were used to determine the animals' reactivity to cocaine. More ambulations and rears indicate a greater reactivity to the drug.
The MP treated rats showed significantly more rears and ambulations than the control rats. These results are interpreted to mean that the effects of cocaine administration on the MP treated rats are greater then rats that did not receive MP. This suggests that MP does indeed cause cross-sensitization with cocaine.
The answer to this question is no. One important factor to note, is that in order for cross-sensitization to occur, the "high" felt from a drug must be similar to another drug. The "high" resulting from MP is a result of MP being taken in a manner other then orrally. When MP is taken orally it takes too long to reach its peak concentration for any type of noticable high to be felt.
Another important fact to note is that dose matters. The results shown above are from rats that received daily administrations of MP in concentrations greater than those prescribed for human usage. The same study tested if MP at low doses (similar to the dose level used in human therapeutic applications) in adolescence would cause enhanced reactivity to cocaine. The results are shown here:
The results show that rats treated with MP and saline had very similar responsivity to cocaine. These results can be interpreted to suggest that when MP is taken at its prescribed therapeutic levels there is little potential for sensitization to cocaine to occur.