How long does it take for the drug MCAT to leave my system, and when will I feel myself again?

MCAT? Mephedrone, also known as 4-methylmethcathinone (4-MMC), or 4-methylephedrone, a synthetic stimulant drug of the amphetamine and cathinone classes?

In what country are you situated and how did you obtain the MCAT?

Proper identification of the drug (often varies by country) and source (purity) are essential to determining elimination rate.

In short, MCAT (synthetic) is man-made and little is known of pharmacokinetics (how the body processes it).

I derive from you question that you are concerned with how long it will take to return to feeling normal (as opposed to how long the drug is detectable). Should be soon based on psychodynamics (thinking processes) of stimulants.