I can't speak to long term effects, I only took it a few times at intervals of a few months. In my experience, MDMA is the opposite of addictive - if you've had a good night on it, taking more will do nothing for you for a few weeks.
https://www.theguardian.com/commentisfree/2015/dec/08/is-ecs...
http://www.telegraph.co.uk/news/uknews/law-and-order/4537874...
David Nutt has spoken widely and very entertainingly about drugs and their relative harms. This is an excellent lecture he has done a number of places on politics and drug policy:
https://www.youtube.com/watch?v=gkcO_wJ9yKo&spfreload=10
Nutt also founded the Independent Scientific Committee on Drugs:
This is a very good source for accurate information about drug risks and harm reduction.
Citation needed.
Risk factors: Certain drugs. Medications that increase your risk of hyponatremia include thiazide diuretics as well as some antidepressants and pain medications. In addition, the recreational drug Ecstasy has been linked to fatal cases of hyponatremia. http://www.mayoclinic.org/diseases-conditions/hyponatremia/b...
While staying hydrated can reduce the risk of heat stroke associated with MDMA, the drug can also cause the body to retain water, so drinking too much can lead to a potentially fatal electrolyte imbalance. http://healthland.time.com/2013/09/03/concert-deaths-five-my...
More common, ecstasy has led to serious hyponatremia and hyponatremia-associated deaths. Hyponatremia in these cases is due to a "perfect storm" of ecstasy-induced effects on water balance. Ecstasy leads to secretion of arginine vasopressin as well as polydipsia as a result of its effects on the serotonergic nervous pathways. Compounding these effects are the ready availability of fluids and the recommendation to drink copiously at rave parties where ecstasy is used. The effects of ecstasy on the kidney as well as therapeutic measures for the treatment of ecstasy-induced hyponatremia are presented. http://www.ncbi.nlm.nih.gov/pubmed/18684895
Additional risk factor: Poorly thought out radio contests:
"A 28-year-old woman found dead hours after taking part in a radio station's water-drinking contest died of water intoxication, the coroner's office said Saturday" [1]
[1] http://articles.latimes.com/2007/jan/14/local/me-water14
You're just plain wrong here. Ecstasy is a dangerous drug that can cause overheating, dehydration, and other very serious conditions that can and do result in death. Further, the drug's effects discourage the behaviors, like eating and drinking water in reasonable quantities, that are essential to preventing those conditions. With their sense of hunger and thirst totally haywire, some people try to overcompensate and end up dying from too much water.
And as for the long-term effects of regular MDMA use: persistent brain damage and loss of cognitive function.