For most men and women MDMA is not typically associated with actual intercourse. The two main reasons for this are that it blocks erection in a large portion of the male population and that the feelings elicited in many people are more appropriate to cuddling than to sex.

Heart issues: Perhaps the most dangerous possible interaction between Viagra and MDMA is the theoretical risk that Viagra's vascular effects could interact dangerously with MDMA's heart-rate, blood pressure, and body temperature-increasing tendencies. MDMA is a strong stimulant, increasing heart rate, blood pressure, and body temperature. Sildenafil, on the other hand, is a vasodilator and reduces blood pressure systemically

MDMA is unambiguously neurotoxic in lab animals in high doses. Typical dose regimens which elicit neurotoxicity are 20 mg/kg (rats) or 5 mg/kg (primates) given twice daily for four days either i.m. (intramuscularly) or s.c. (subcutaneously). Humans typically use MDMA p.o (per oral) and at levels of about 2.5 mg/kg or less. One study of MDMA administered to primates most closely modelled human use and used doses of 2.5 mg/kg given every 2 weeks for 4 months (2.5 mg/kg x 8) which found no evidence of neurotoxicity

This MDMA effect dropoff might be explained by a psychological mechanism: loss of novelty. (On the other hand, people who have experienced MDMA effect dropoff generally report that there is not a similar dropoff in the effects of other psychedelics with which they are equally or more experienced, e.g. LSD and DMT.) Or the dropoff might be caused by lasting neurophysiological or neurological "changes" to the brain from exposure to MDMA, the prior state of the changed structures being necessary for ecstatic MDMA experiences. It is an as-yet-unanswered question whether such changes, if they happen, are best regarded as harmful, neutral, or beneficial.

Note that MDMA is not known for causing strong visual distortions. If you take some "MDMA" and notice that a predominant effect is trippy visuals, what you got was probably not pure MDMA, or MDMA at all.

Entactogenesis ("touching within") - a generalized feeling that all is right and good with the world. Empathogenesis - a feeling of emotional closeness to others (and to one's self) coupled with a breakdown of personal communication barriers. MDMA can significantly enhance (sometimes distort) the senses - touch, proprioception, vision, taste, smell. MDMAers can sometimes be seen running their hands over differently textured objects repeatedly, tasting and smelling various foods/drinks.

The euphoria that it induces can make it easy to ignore bodily distress signals, so be watchful for things like dehydration (drink lots of water or fruit juices!), muscle cramping, dizziness, exhaustion or overexertion