The responsible drug user is a myth created to sell more drugs. Most illegal drugs are both addictive and tolerance causing. It is certainly true of MDMA. That means you will not get the same effect, from the same amount next time. You will have to increase your dosage to get the same or similar experience.

So you either stop using the drug (if you are lucky) or go on a downward spiral of higher doses, more negative side effects and life deterioration.