An erection is achieved when blood is pushed into the penis to increase its size and hold pressure within it. This isn’t actually common in mammals, and humans are one of the only mammals which don’t have a penis bone, called a baculum. Penis bones keep the penis constantly erect, but can retract back into the body after sex. Evolutionary biologists believe that humans don’t have this bone because becoming erect through hydraulics is a “fitness indicator” to potential mates, indicating the cardiovascular health of their sexual partner.

Because of this hydraulic penis, achieving and maintaining an erection becomes a little more complicated. Multiple chemicals are involved, one of which is nitric oxide.

Nitric Oxide in Erections

An erection involves three main processes:

  1. Smooth muscle relaxation.
  2. Arterial dilation.
  3. Venous constriction.

When a man becomes aroused, the smooth muscles inside the penis which contain penile blood vessels (called the corpora cavernosa) relax, allowing the arteries inside to open. Blood enters the penis and fills the penis, causing it to become erect. The vessels leading to the penis are then compressed by pelvic floor muscles (also called kegels), trapping the blood.

Nitric oxide is a principal agent responsible for the vasodilation, as it is involved in the relaxation of the smooth muscle. If the smooth muscle remains tense, it compresses the corpora cavernosa and prevents blood from entering it. Nitric oxide deficiency has been shown to be a potential cause of ED in some patients, as well as vascular diseases, which may be why 40% of men over 40 with the symptoms of ED also suffer from cardiovascular disease.

Nitric Oxide Supplements

Common nitric oxide supplements include:

  • L-citrulline
  • L-arginine
  • French maritime pine bark extract
  • Nitrates

Nitric oxide supplements, and natural nitric oxide boosters like ginkgo biloba are popular supplements for ED. The science on the effectiveness of these supplements is debated, and while nitric oxide deficiency can definitely cause ED, different research has produced different results as to whether supplements are effective or not

You should always consult your doctor before taking supplements like these, particularly alongside PDE5 inhibitors like Viagra. Combined with PDE5 inhibitors, nitrates can cause your blood pressure to drop quite quickly, causing headaches, dizziness, and potentially even causing you to pass out.

What Else Does Nitric Oxide Do?

Nitric oxide is naturally produced in the body by the endothelium, which is the lining of blood vessels. The chemicals which the endothelium excretes are affected largely by the chemical composition of the blood running through it. More nitric oxide is released when the endothelium senses chemical indicators of physical exercise and low levels of cholesterol, so if you want to increase your natural nitric oxide levels without supplements or medication, your best bet is to start with regular exercise, a healthy diet and quitting smoking. 

As well as helping you achieve erections, nitric oxide also expands other blood vessels, decreasing blood pressure, plaque growth and risk of blood clotting. It stimulates the release of hormones like insulin and human growth hormone, and can improve fitness by increasing the amount of oxygen that can be delivered to the muscles. It’s pretty important for your general health, so it is in your best interest to ensure you have healthy levels of it.