wait you mean dopesick from lack of methadone? (if it is methadone then please do not take MDMA near methadone as 'done can actually contribute to serotonin syndrome) or are you meaning IVing methamphetamine? (im aware some use meth for opioid w/ds to be fair)
You should do the X pills orally ideally, or rectally if nausea is an issue. Intranasal is short acting, more likely to cause unwnted bodyload and nausea IME, and a lot edgier/less euphoric. Also if youre gonna snort MDMA at least snort MDMA xtal not MDMA cut with pill binders.
The issue is its not sustainable taking MDMA regularly whereas other amphetamines, while still having diminishing returns, dont cause nearly as much damage from semi/regular use and wont fall off so quickly in effect.
Also are you using reagents tests to find out if its actual MDMA.
MDMA can cause nausea irrespective, this is because serotonin itself does and mdma obv releases a load of it. the serotonin receptor 5ht3 is recsponsible for emesis response in the gut and the nausea center in the brain. Serotonin agonising this heavily can cause the aforementioned physiological reactions.
Anti emetics might be a good shout. Ginger or peppermint are good for nausea. Things containing the terpene beta-pinene such as essential lemon oil (or lemon peel, not flesh) and cannabis are antiemetic. The most potent and selective 5ht3 antagonist we have available is a pharmaceutical called Zofran (generic name Odansetron) which does practically nothing else except block 5ht3. Everyone i know that uses it says its a godsend. Its generally prescribed for morning sickness but its probably pretty easy to wangle a subscription cos its not abusable and has a very forgiving safety profile, it interacts with not very much other than the things youre taking it to block (it wont even block psychedelic effects or the mdma euphoria like a lot of other serotonergic antagonists which would usually block a lot of 5ht receptors, not just 5ht3).