Bad

Herpes: There is a concern that L-arginine might make herpes worse. There is some evidence that L-arginine is needed for the herpes virus to multiply.

Low blood pressure: L-arginine might lower blood pressure. This could be a problem if you already have low blood pressure.

Recent heart attack: There is a concern that L-arginine might increase the risk of death after a heart attack, especially in older people. If you have had a heart attack recently, don't take L-arginine.

Kidney disease: L-arginine has caused high potassium levels when used by people with kidney disease. In some cases, this has resulted in a potentially life-threatening irregular heartbeat.

Surgery: L-arginine might affect blood pressure. There is a concern that it might interfere with blood pressure control during and after surgery. Stop taking L-arginine at least 2 weeks before a scheduled surgery.