Given it's interactions with caffiene it makes some sense to me it could cause diarrhea. Caffiene will do it on its own, but if you combined it with the ephedra it could do a double whammy.Here is the warning from metabolifes own web page:I got one word for this: YIKES!WARNING: NOT FOR USE BY PERSONS UNDER AGE 18. DO NOT USE IF PREGNANT OR NURSING. CONSULT A PHYSICIAN OR LICENSED QUALIFIED HEALTH CARE PROFESSIONAL (�PHYSICIAN�) BEFORE PRODUCT USE IF YOU HAVE, OR HAVE A FAMILY HISTORY OF, HEART OR THYROID DISEASE, DIABETES, HIGH BLOOD PRESSURE, RECURRENT HEADACHES, DEPRESSION, ANY PSYCHIATRIC CONDITION, GLAUCOMA, DIFFICULTY URINATING, ENLARGED PROSTATE, SEIZURE DISORDER, IF YOU ARE USING A MONOAMINE OXIDASE INHIBITOR (MAOI) OR ANY OTHER DIETARY SUPPLEMENT, PRESCRIPTION DRUG OR OVER-THE-COUNTER DRUG CONTAINING EPHEDRINE, PSEUDOEPHEDRINE OR PHENYLPROPANOLAMINE (INGREDIENTS FOUND IN CERTAIN ALLERGY, ASTHMA, COUGH/COLD, AND WEIGHT CONTROL PRODUCTS), OR IF YOU INTEND ON TAKING TO REDUCE WEIGHT. THE MAXIMUM RECOMMENDED SERVING OF EPHEDRINE FOR A HEALTHY ADULT IS 100 MG IN A 24 HOUR PERIOD FOR NOT MORE THAN 12 WEEKS. EXCEEDING RECOMMENDED SERVING MAY CAUSE SERIOUS ADVERSE HEALTH EFFECTS INCLUDING HEART ATTACK AND STROKE. DISCONTINUE USE AND CALL A PHYSICIAN IMMEDIATELY IF YOU EXPERIENCE RAPID HEARTBEAT, DIZZINESS, SEVERE HEADACHE, SHORTNESS OF BREATH, OR OTHER SIMILAR SYMPTOMS. INDIVIDUALS WHO CONSUME CAFFEINE WITH THIS PRODUCT MAY EXPERIENCE SERIOUS ADVERSE HEALTH EFFECTS. KEEP OUT OF THE REACH OF CHILDREN.