The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Creatine has been associated with asthmatic symptoms. People should avoid creatine if they have known allergies to this supplement. Signs of allergy may include rash, itching, or shortness of breath.
Side Effects and Warnings
There is limited systematic study of the safety, pharmacology, or toxicology of creatine. Individuals using creatine, including athletes, should be monitored by a healthcare professional. Users are advised to inform their physicians or other qualified healthcare professionals.
Some individuals may experience gastrointestinal symptoms, including loss of appetite, stomach discomfort, diarrhea, or nausea.
Creatine may cause muscle cramps or muscle breakdown, leading to muscle tears or discomfort. Strains and sprains have been reported due to enthusiastic increases in workout regimens once starting creatine. Weight gain and increased body mass may occur. Heat intolerance, fever, dehydration, reduced blood volume, or electrolyte imbalances (and resulting seizures) may occur.
There is less concern today than there used to be about possible kidney damage from creatine, although there are reports of kidney damage, such as interstitial nephritis. Patients with kidney disease should avoid use of this supplement. Similarly, liver function may be altered, and caution is advised in those with underlying liver disease.
In theory, creatine may alter the activities of insulin. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Serum glucose levels may need to be monitored by a healthcare professional, and medication adjustments may be necessary.
Long-term administration of large quantities of creatine is reported to increase the production of formaldehyde, which may potentially cause serious unwanted side effects.
Creatine may increase the risk of compartment syndrome of the lower leg, a condition characterized by pain in the lower leg associated with inflammation and ischemia (diminished blood flow), which is a potential surgical emergency.
Reports of other side effects include thirst, mild headache, anxiety, irritability, aggression, nervousness, sleepiness, depression, abnormal heart rhythm, fainting or dizziness, blood clots in the legs (called deep vein thrombosis), seizure, or swollen limbs.
Pregnancy and Breastfeeding
Creatine cannot be recommended during pregnancy or breastfeeding due to a lack of scientific information.
Pasteurized cow's milk appears to contain higher levels of creatine than human milk. The clinical significance of this is not clear.