from erowid
NEGATIVE
(negative side effects increase with higher doses and frequent use)
* inappropriate and/or unintended emotional bonding
* tendency to say things you might feel uncomfortable about later
* mild to extreme jaw clenching (trisma), tongue and cheek chewing, and teeth grinding (bruxia)
* difficulty concentrating & problems with activities requiring linear focus
* short-term memory scramble or loss & confusion
* muscle tension
* erectile disfunction and difficulty reaching orgasm
* increase in body temperature, hyperthermia, dehydration (drink water)
* hyponatremia (don't drink too much water)
* nausea and vomiting
* headaches, dizziness, loss of balance, and vertigo
* post-trip Crash - unpleasantly harsh comedown from the peak effect
* hangover the next day, lasting days to weeks
* mild depression and fatigue for up to a week
* severe depression and/or fatigue (uncommon)
* possible strong urge to repeat the experience, though not physically addictive
* possible psychological crisis requiring hospitalization (psychotic episodes, severe panic attacks, etc) (rare)
* possible liver toxicity (rare)
* possible neurotoxicity (controversial)
* small risk of death. Approximately 2 per 100,000 users have extreme negative reactions resulting in death. (rare)