Consider taking L-arginine. This is an amino acid that leads to increased blood flow, helping the penis get larger during an erection. A study conducted at Tel Aviv University showed that some men experienced improvements after taking the supplement for 6 weeks. It's available in natural food stores, and the recommended dose is 1 gram three times a day.[4]
This supplement should not be taken if you're on nitroglycerin for your heart, because it can cause a drop in blood pressure. Talk with your doctor about whether you should take L-arginine.[5]