L-arginine can worsen allergies or asthma. Use the supplement with caution if you have these conditions. Be careful about taking L-arginine if you've had cold sores or genital herpes. Too much L-arginine in your system can potentially trigger the virus that causes those conditions.

When should you not take L-arginine?

Risks. If you have any medical conditions -- like cancer, asthma, allergies, liver or kidney problems, low blood pressure, sickle cell disease, or a bleeding disorder -- or have had a heart attack, don't take arginine without talking to a doctor first.

Why is arginine bad?

In clinical trials, arginine has been used safely with minor side effects for up to three months. Possible side effects include abdominal pain and bloating, diarrhea, and gout. It may also cause a worsening of breathing in people with asthma. Arginine may interact with certain medications that lower blood pressure.