5-HTP
Take pre and post roll.
The obvious one. Serotonin precursor, good for getting the most out of your roll and restoring SERT levels afterward.
B6
Take pre and post roll.
Facilitates synthesis of serotonin from 5-HTP.
Tyrosine
Take pre and post roll.
Same as 5-HTP, but for dopamine, norepinephrine (noradrenaline) and epinephrine (adrenaline). You could also take L-DOPA, but that is a bit more dangerous and could give you stimulant psychosis if you take too much. DLPA is the precursor to tyrosine
Antacids
Take pre roll.
Milk of magnesia, tums, pepcid AC, alka seltzer, etc. Lets more of your roll be absorbed in the small intestines since less is broken down on the way there. You can get around all of this by plugging, but that's kind of gross.
Magnesium
Take pre roll, and every day.
Keeps you from grinding your teeth if you get that. Also, this is an NMDA receptor antagonist, which should reduce your tolerance to stimulants in general. Anti alzheimer's meds may be more effective at this, but are probably more dangerous, and you shouldn't steal your grandma's medicine.
Alpha Lipoic Acid
Take pre roll.
Antioxidant. This will protect your brain from MDMA neurotoxicity.
Vitamin C
Take pre roll.
Another antioxidant. The idea that it increases a roll's intensity seems to be a myth. This should be coupled with antacids so you don't reduce your roll's potency.
Acetyl-L-Carnitine
Take pre roll.
Yet another antioxidant that has been shown to protect against MDMA neurotoxicity.
Cannabis
SMOKE WEED EVERY DAY
This attenuates hyperthermia, which will protect your brain from MDMA neurotoxicity. Take as much of this supplement as possible :)
OPTIONAL SHIT/ACCESSORIES
This stuff might make your rolling experience better, but isn't specific to MDMA or anything.
B12
Deficiency causes energy loss. Good for a slight energy boost. (if you're into nitrous, you need to be taking this)
Piracetam
One of many nootropics. Piracetam's effects and mechanisms are not fully understood. It seems to increase blood flow between the hemispheres of the brain, but this could be a side effect and not its primary action. It improves the function of acetylcholine via Ach receptors. In any case, this will potentiate your roll a little (along with anything else you took). It should be noted that this will heavily potentiate alcohol.
Choline
Comes in various forms, such as choline bitartrate. This is a necessary supplement when taking piracetam because it depletes acetylcholine, a very essential neurotransmitter.
Buproprion
Better known as wellbutrin. This is a selective dopamine reuptake inhibitor. It's prescribed for a number of things (anxiety, depression, smoking cessation, ADHD....), but essentially it's a long lasting, mild stimulant with an incredibly gentle comedown. If you can get your hands on some, it's great for feeling better the day after. More effective than 5-HTP in my experience. DON'T TAKE TOO MUCH OF THIS, more than 450mg/day can cause seizures.
WARNING
Just because something is a supplement does not mean it is totally innocuous. don't take too much 5-HTP, tyrosine, antacids, magnesium, piracetam, choline, or buproprion. AFAIK B6, B12, and C can't be OD'd on. Not sure about ALA or A-l-C. Ofc, smoke as much weed as you want.
W/R/T Neurotoxicity
It's kind of up in the air. No one is totally sure if MDMA causes any cognitive deficits, or permanent damage, or even any physical damage at all. What we do know is heavy MDMA use results in less SERT (serotonin transporter)floating around, which isn't a good thing. This could be evidence of physical damage, or permanent downregulation of its production, or just temporary downregulation. But people generally seem to think there's some actual damage going on, if you take a shitload of MDMA you're definitely playing with fire, so be warned.