While 5-HTP, in a pure form is not a risk for EMS, there are some cautions to be observed in it's use. 5-HTP should not be used if you have the following medical conditions:

Cardiovascular Diseases; Extremely Elderly Persons; those with Parkinsons; Disease, Cancer or Autoimmune Diseases; Lung Diseases; Chronic Alcoholism; Liver diseases; parasitic infection; AIDS; Anorexia Nervosa; Low protein Diets; Severe allergies; Myalgia; Peripheral Neuropathy; Rash or Flushing; Edema; Nausea; Diarrhea; Sickle cell anemia; hemophilia; Pregnancy

Do not use 5-HTP is you are currently taking any of the following medications:

Anti-depressant drugs; Monoamine oxidase inhibitors; Selective Serotonin Reuptake Inhibitors; Tricyclic medications; Weight Loss medications; Anti-parkinson medications; Barbiturates and other tranquilizing drugs; Antihistamines and cold medications; Alcoholic beverages; Intravenous drugs; Cancer chemotherapy or antibiotic medications.

Warning:

Dosages of 5-hydroxy L-tryptophan (5-HTP) greater than 100 milligrams per day should be taken only under the guidance of a physician. 5-HTP use at doses greater than 100 mg per day should be taken with the prescription drug carbadopa to prevent excessive levels of serotonin production in the peripheral blood circulation. 5-HTP can increase the effect of tranquilizing drugs and can impair the ability to drive an automobile.

From: http://depression.about.com/cs/altmed5htp/f/5htp.htm