Molly is a slang term for powdered MDMA. It used to mean pure MDMA powder, however now it's often sold with an inactive cut added to it for reasons of greed.

MDMA is an empathogen, entactogen, psychedelic, stimulant, and a whole lot of other things all rolled into one little chemical. MDMA itself is a slang term, short for 3,4-methylenedioxy-methamphetamine. It acts in various ways on your serotonin, dopamine, norepinephrine, and other major neurotransmitter systems, although most scientific study has been focused on its effects on serotonin.

There is no science that suggests that occasional MDMA usage in the comfort of the home or therapist's office will cause any long term problems for anyone. MDMA as well as Adderall (DL-amphetamine) are both known to be neurotoxic, in that they cause damage to certain brain cells under certain situations, but Adderall and methamphetamine are a bit more neurotoxic than MDMA.

That doesn't prevent them from prescribing high doses of Adderall to millions of children though, so I see no reason why it should prevent intelligent people from feeling that their health is safe when taking MDMA in a responsible manner.

Raised body temperature is known to make the neurotoxicity of these stimulants worse, so dancing indoors all night, drenched in sweat, on MDMA is about the worst possible way to keep your brain safe when using MDMA.

If you are unsure about your MDMA or molly, I recommend buying an Ecstasy Test Kit like the following:

http://www.bluelight.ru/vb/testkits.php

These testing kits can be used to determine whether the pill or powder you were sold is the real deal, or a dangerous substitute or fake. Let your friends know you have the kit, and encourage them all to test their pills before using them. You never know when you're going to get sold pills with PCP or PMA or something in them.