MDMA's primary action is on serotonin transporters and receptors, but it ultimately leads to a greater increase in dopamine.
The serotonin network suppresses dopamine in 3 of the 4 dopamine pathways.
The major reward pathway, the meso-limbic, is the exception.
When the peak hits, serotonin has reached its maximum level and begins to fall along with cortisol.
This suggests that it is a DROP in serotonin that causes the 'magic' to happen - because dopamine suppression has been lifted and the meso-limbic reward pathway has been targeted with a SURGE of dopamine. As the other dopamine pathways are allowed to fire again, the meso-limbic is PRIMED for action. Cue pituitary release of oxytocin and prolactin!
Dopamine in the meso-limbic pathway is what makes ALL drugs worth doing.
And stimulants like METH release FAR more dopamine than MDMA.
This means they can down-regulate dopamine receptors in this critical pathway!
And kill dopamine neurons, esp. in the nigro-striatal pathway.
The death of dopamine activity is the cause of this problem.
I could simply have said 'cross-tolerance' happens, but I felt a longer explanation is warranted.
MDMA can damage dopamine neurons, but the serotonin network is MUCH more fragile.
Taking MDMA is more likely to cause 'brain damage' than meth, but all drugs can cause this in the right repeated doses.
I have ONE friend who uses METH and he can NEVER roll.
In fact, he has said that the day after he feels WAY fucked up.
His chest hurts...he thinks he isn't breathing right...
He doesn't see the point.
And animal studies have shown that METH increases the toxicity of MDMA to serotonin neurons considerably.
A central theory of MDMA toxicity involves the metabolites of dopamine finding their way into the serotonin receptors.
Meth users shouldn't be trying to roll.
Period.
They shouldn't be doing METH either...