Side Effects of MDMA (Molly/Ecstasy)

Read about MDMA's (Molly/Ecstasy) side effects, including anxiety, dizziness and feeling cold during use.

New to or MDMA? Check out our overview page.

MDMA's (Molly/Ecstasy) Side Effects

To learn how pure Molly (MDMA) makes you feel, visit this page.

Side effects of pure MDMA

Possible side effects during use

  • Dry mouth
  • Difficulty concentrating
  • Anxiety
  • Feeling cold
  • Impaired balance/gait
  • Heavy legs
  • Jaw clenching/tight jaw
  • Lack of apppetite
  • Perspiration
  • Thirst
  • Restless legs

“Overall, adverse effects of MDMA are modest and generally have not been associated with serious discomfort in healthy volunteers or in people with PTSD.” “Common reactions reported in clinical trials are transient and diminish as drug effects wane during the MDMA session and over the next 24 hours. Once the drug leaves the body, 3 to 4 days post-treatment, most reactions diminish.”1

“There can be acute nervousness or anxiety during the psychotherapy session, but that’s to be expected, because again, that’s the drug bringing out the effects of PTSD. You want to bring up anxiety, but it’s reported as a side effect. There’s also heightened cardiovascular activity - you might get a slightly higher heart rate or a slightly higher blood pressure level. But in all our studies so far, we’ve kept the blood pressure constant to that of the room. Out of the 136 subjects who were treated in the Phase 2 studies, only one 50-year-old male had an elevated heart rate. The physician on-site decided, “Oh, we’re not so sure about this,” so the patient went to the emergency room and was released later that day with no treatment. That’s the worst case we’ve seen in all of the trials.”2

“MDMA has been administered to more than 750 human subjects in clinical studies with only one single serious adverse event occurring as a result of the drug.”3

Details of the single serious adverse effect: “One related serious adverse reaction has occurred within all sponsor-supported studies to date. Subject 0811 experienced an increase in frequency of ventricular extrasystoles (PVC’s), a form of arrhythmia, on the day of his third and final experimental session with open-label 125 mg MDMA. The subject had no other signs and no symptoms of cardiac distress. In the absence of any symptoms of coronary insufficiency, the investigator judged the only medical measure necessary to be withholding the supplemental dose of MDMA.” “Full recovery occurred 1 day after MDMA administration.”1

Side effect during use Average proportion of MDMA clinical trial participants who experienced this side effect, increase over placebo group1
Anxiety 19%
Difficulty concentrating 37%
Dizziness 41%
Drowsiness -24%
Dry mouth 64%
Fatigue -11%
Feeling cold 39%
Weakness 16%
Headache 11%
Heavy legs 38%
Impaired balance/gait 44%
Insomnia 17%
Jaw clenching/tight jaw 60%
Lack of apppetite 66%
Lack of energy 0%
Muscle ache/tension 20%
Nausea 17%
Rapid eye movements 23%
Skin tingling 22%
Ruminations 15%
Perspiration 40%
Feeling cold 31%
Thirst 44%
Restless legs 45%
Palpitations 37%
Feeling hot 23%
Jaw muscle spasms 21%
Tension 18%
Urge to urinate 7%
Tremor 22%
Forgetfulness 15%
Brooding 12%

Serious acute risks

About 2.66 million people used ecstasy in the US in 2015.4 5 Harm reduction expert Emanuel Sferios estimated that there are around 20 ecstasy related deaths per year in the US. This is 0.00075% of users. For comparison, there’s a “0.0007% chance of dying from a skydive, compared to a 0.0167% chance of dying in a car accident” based on driving 10,000 miles.6

Short-term risks:

  1. Consuming a substance that is not MDMA. Many tablets and powders are fake and/or adulterated with other drugs.7 8 9 10
  1. Heat stroke and/or serotonin syndrome. Like all serotonergic drugs, MDMA increases heat stroke risk due to its effects on the hypothalamus, the part of our brain that helps us regulate body temperature.11
  1. Hyponatremia. Generally caused by drinking too much water. MDMA causes water retention.12 Dancing aerobically in hot environments causes dehydration. Overcompensating by drinking too much water can be fatal.

Possible side effects during the next few days

“Common reactions reported in clinical trials are transient and diminish as drug effects wane during the MDMA session and over the next 24 hours. Once the drug leaves the body, 3 to 4 days post-treatment, most reactions diminish.”1

  • Decreased appetite1
  • Dizziness1
  • Immune functioning: “MDMA may also produce modest changes in immune functioning, lasting up to 48 hours.”3

“During the week after each experimental session, the most commonly reported reactions at any severity were anxiety, fatigue, insomnia, depressed mood, hypersomnia, difficulty concentrating, decreased appetite, and dizziness in the active dose MDMA groups across studies, with PTSD studies overrepresented. Of these reactions, only decreased appetite and dizziness were appreciably elevated above the placebo group, and the remaining reactions are likely to be background events.”1

The comedown

Interestingly, in MAPS sponsored MDMA clinical research, depressed mood in days 1-7 following MDMA use was observed in 13% of patients in the placebo condition, and 13% of patients in the 100-125 mg condition! Refer to page 77 of 143.1

From the fantastic book Acid Test: “He’d learned that MDMA, which flooded the brain with serotonin during the session, could leave a hangover of serotonin depletion for a few days, which might be associated with depressed feelings. Oddly though, in Michael’s first study, the subjects who took only the sugar pill reported more depressed feelings following the sessions than those who got the MDMA.”13

Anecdotal reports indicate that “comedowns” are strongly related to:

  • Impure MDMA
  • Unsafe dosages
  • Not waiting long enough between MDMA uses
  • Lack of sleep14
  • Lack of healthy diet/exercise/lifestyle

Possible long-term side effects


Does MDMA cause brain damage? Two researchers who reviewed animal and human studies as of the year 2000 concluded that frequent or heavy use “may exhaust neuronal energy sources and antioxidant defenses, leading to damage.” They warn that “the possible risks of neurotoxicity must be considered when assessing the potential administration of MDMA to humans.“45

One of those researchers, Matthew Baggott, points out that since the year 2000, millions of Americans have continued to use illicit MDMA and its popularity remains on the rise among young people.”

“I am slightly reassured,” Baggott said, “that we haven’t seen an obvious epidemic of mental health problems despite thirty years of widespread MDMA use. But we absolutely still need to consider potential neurotoxicity when considering giving MDMA to people.”15

MDMA researcher Matthew Baggott: “To the best of my understanding, doses around 1.5-1.7 mg/kg MDMA (roughly 100 to 125 mg MDMA) are unlikely to cause long-lasting serotonin changes. Studies by MAPS have looked for changes in mental abilities after people participated in their studies, with some participants receiving 125 mg followed by 62.5 mg, and have not found any changes.” MAPS study protocol involves 3 - 5 week breaks, and a total of 2 or 3 MDMA sessions in total.

Advocates of MDMA-assisted psychotherapy stress the differences between heavy recreational drug users and patients who are carefully screened and take the medication two or three times in a supervised setting. Statistics from emergency room visits or reports of deaths attributed to Ecstasy are troubling, but they often involve users who may be simultaneously drinking alcohol and ingesting other illicit drugs. Those behind the new wave of studies point out that more than a thousand people have received MDMA in research settings without any serious problems. “There is little reason to fear,” says Rick Doblin of MAPS, the psychedelic research sponsor, “that normal therapeutic (or recreational) doses of MDMA will result in harmful functional or behavioral consequences.”15

Since the MDMA dosage Ricaurte had tested was about three times the average therapeutic dose equivalent—1.7 milligrams per kilogram—Rick urged him to do another test at a lower dosage to determine if, at any point above the therapeutic dosage, MDMA would show no long-lasting effect on serotonin neurons anywhere in the brain. That point came at 2.5 milligrams per kilogram, still 50 percent above the usual therapeutic dosage. Eight doses of that size were administered over four months (one dose every two weeks), after which there was no detectable damage to neurons. Rick was greatly relieved, since that would be the key to persuading the FDA that it would be safe enough to conduct human therapeutic trials.”13

Why is there confusion and false information surrounding MDMA? Read this by Rick Doblin, founder of MAPS.


“No significant differences in cognitive function were detected at the 2-month follow-up between subjects who received two sessions with 125 mg of MDMA compared to subjects who received placebo, as measured by RBANS and PASAT.” See page 60 of 143.1

“In a study designed to minimize limitations found in many prior investigations, we failed to demonstrate marked residual cognitive effects in ecstasy users. This finding contrasts with many previous findings—including our own—and emphasizes the need for continued caution in interpreting field studies of cognitive function in illicit ecstasy users.”14

“Overall, differences between non-users and heavy users were sufficiently modest on most cognitive measures that we could exclude a large effect of ecstasy (d ≥ 0.8) at the 0.05 level.”14

“Conversely, our present findings appear congruent with several other recent studies suggesting that cognitive effects of ecstasy use are modest (16, 58) and perhaps mediated or confounded by trait impulsiveness (47), comorbid substance use (48), and sleep deprivation (48, 59)—although this last possibility remains uncertain (60).”14

Extra info from

A very relevant thing that stands out in the science concerning MDMA, is that studies using people with a history light and occasional use of MDMA are far less likely to show mental deficits compared to studies where people have a history of binging on large amounts of MDMA or regular MDMA use. Whether or not deficits are caused by lack of sleep or use of other drugs, it is still the case that partying too hard may affect your mental abilities.

There is scientific controversy over the long term harmful effects of MDMA. Although, studies with MDMA users have found impairments in memory and impulsivity, there are other factors which may contribute to this, such as use of other drugs and lack of sleep. Controlling for such things, one particular study found no significant connection between MDMA use and performance on cognitive tests, although this study has received some criticism

It is also possible that something like impulsivity could make someone more likely to take MDMA, rather than being caused by MDMA use (summarised in this article). A similar confusion is found with the link between MDMA and depression. Some studies have suggested that MDMA can contribute to depression, though some have found that those with depression may be more likely to later take MDMA.

Whether such effects would last for a very long time is also debatable. There is strong evidence from brain imaging studies suggesting that most changes in the brain areas affected by MDMA (serotonergic system) are not long term.

For most people, it is hard to know what to think when considering the possible long term harms of MDMA. One thing that you need to consider, is that a statistically significant effect on memory in a study, may reflect a very subtle (but possibly significant) effect on everyday life. Effects being subtle however, may also mean that effects on mental abilities caused by MDMA could go unnoticed. It is therefore very difficult to know if MDMA would affect you, or whether such effects would be a problem. Additionally, although the long term effects of MDMA may be less risky than something like tobacco, there is no way to know if what is bought illegally is actually MDMA.

There is also anecdotal evidence that after multiple uses of MDMA, the ‘magic goes’ and users no longer find the drug as enjoyable (although this is not reported by all).

Side effects of MDMA (Molly, Ecstasy) relative to other drugs

A 2010 research paper compares the harms of various drugs “using multi-criteria decision analysis (MCDA) – a method that uses relevant experts’ knowledge and experience to assess the actual and relative harms.”16 This involved looking at the side effects of each drug and comparing them.

Relative side effects of MDMA

The blue bars (harm to users) are independent of the popularity of the drug, while the red bars (harm to society) are dependent on the popularity of the drug. Even if the same number of people used MDMA as use alcohol, their blue bars/harm to users scores would still be the same.16

“Finally, we should note that a low score in our assessment does not mean the drug is not harmful, since all drugs can be harmful under specific circumstances.”17

Side effects of impure MDMA (very common with Molly or Ecstasy)

Millions of MDMA users put themselves at unnecessary risk by using impure MDMA. The chemicals that are often mixed with or sold as MDMA are often higher risk than MDMA.10 17

Unfortunately, your “MDMA”, “Molly” or Ecstasy is probably not pure MDMA. This 2005 paper found that 61% of tested ecstasy tablets contained other drugs. And a massive 46% contained 0% MDMA.10

87% of “Molly” analyzed by the DEA between 2009 and 2013 contained 0% MDMA, instead mostly containing “bath salts.”7 😔

These other substances that are mixed in with MDMA can have worse side effects than pure MDMA - as the image above makes clear. Most illicit drugs have a greater risk of serious harm than MDMA, and so getting impure MDMA substantially increases your risks. And given that illegal drugs have no regulation, impure MDMA is a very frequent risk.7

Read more about the risk of impure MDMA and how to partially address it with a test kit.

Learn next

How does Molly (MDMA) make you feel?


  1. MDMA Investigator’s Brochure (2016) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2.,-but-now-it-needs-to-leap ↩︎

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  10. Pharmacological content of tablets sold as “ecstasy”: Results from an online testing service ↩︎ ↩︎ ↩︎

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  17. Nutt, D. J., King, L. A., & Phillips, L. D. (2010, November 01). Drug harms in the UK: A multicriteria decision analysis. The Lancet, 376(9752), 1558-1565. doi:10.1016/s0140-6736(10)61462-6 ↩︎ ↩︎

New to or MDMA? Start here.

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Recommended documentary about MDMA therapy: Trip of Compassion.