Does taking extra magnesium help to avoid ritalin (methylphenidate) tolerance?

Unlikely: Drugs such as Ritalin (methylphenidate) have a tendency to develop tachyphylaxis or tolerance over a period of months, and often dosage increase is only temporarily useful. A better plan might be to switch to a similar medication in a slightly different class, and go back to Ritalin (methylphenidate) after 3 months. I am unaware of any success in preventing phenomenon by use of magnesium.