L-arginine is defined as a semi-essential amino acid. That sounds a bit odd -- something is either essential (shelter) or it isn't (cable TV), right?
Sort of. "Essential" has a slightly different meaning in nutrition. An essential nutrient is one that you must obtain somehow, either through diet or through supplements, because your body can't manufacture it on its own [source: Baggott]. L-arginine is described as semi-essential because usually the body produces enough L-arginine on its own [source: MedlinePlus]. But in some cases, such as trauma or liver disease, people can develop deficiencies, and then an L-arginine supplement is called for [source: Drugs.com].
Your body needs L-arginine to make urea, the waste product that you get rid of when you urinate [source: Mayo Clinic]. Urea is a byproduct created when your body breaks down proteins. Your body needs some nitrogen, but the breakdown of protein creates more than you need. Making urea is a very efficient way for your body to get rid of excess nitrogen [source: WebMD]. L-arginine helps your body regulate its waste and certain chemical balances.
L-arginine helps your body manufacture creatine, a protein that contributes to muscle mass and power. L-arginine also helps the body get rid of creatinine, the waste product associated with this process [source: Mayo Clinic]. For these reasons, the bodybuilding industry loves to tout creatine and L-arginine supplements.
Some effects of L-arginine depend on the method in which the body is exposed to the chemical. L-arginine can be administered as a nutritional supplement, inhaled or injected [source: Mayo Clinic]. And, of course, you get some of it through the foods you eat.
When it's administered as a medicine, L-arginine is a vasodilator -- that is, it dilates the blood vessels, allowing more blood to pass through at once. That has the effect of lowering blood pressure and, in some cases, helping the body negotiate the arterial blockages that can come with conditions such as atherosclerosis [source: Mayo Clinic].
To learn about some of the health benefits of L-arginine, read on.