Ritalin (methylphenidate) is a psychostimulant used for the treatment of ADHD and narcolepsy. Ritalin works by inhibiting the removal of dopamine, increasing the amount of dopamine available between brain connections (synapses).
It is inadvisable to mix alcohol (ethanol) with Ritalin because alcohol can increase central nervous system (CNS) side effects associated with Ratlin, including drowsiness, dizziness, depression and seizures. In addition, alcohol may interfere with the delayed release mechanism of some formulations of Ritalin, causing the Ritalin to be released in the stomach too quickly.
That being said, Ritalin and alcohol are not absolutely contraindicated.
One consideration is that since Ritalin is a psychostimulant, it can counteract some of the CNS depressant effects of alcohol, making one feel less drunk. Hence, mixing Ritalin and alcohol may lead to overdrinking or alcohol poisoning by mitigating some of the sedative effects of alcohol. Most people regulate their alcohol consumption by observing how drunk they feel. Ritalin may interfere with this self-regulation.
There is also tentative evidence that alcohol may exacerbate potentially neurotoxic effects of Ritalin by competitively inhibiting aldehyde dehydrogenase enzymatic activity, leading to an accumulation of the reactive and autotoxic intermediate 3,4-dihydroxyphenylacetaldehyde (DOPAL).