L-arginine is an essential amino acid the body uses to make protein. Although L-arginine supplements are generally not necessary, they may provide some health benefits to people with certain medical conditions. The National Institutes of Health notes that L-arginine may improve circulation, reduce blood pressure, treat congestive heart failure and boost recovery after surgery. Despite these benefits, L-arginine is not without some risks. When combined with certain prescription drugs, L-arginine can lead to an unacceptable risk of serious side effects. Do not use L-arginine if you are taking any medications that interact with the supplement.
Antihypertensives, or drugs used to reduce blood pressure, interact dangerously with L-arginine. The National Institutes of Health, which classifies the combination as a "major" interaction, warns of serious side effects when the two products are used together. The combination could cause blood pressure to drop to dangerous levels, leading to uncomfortable or even fatal complications. Do not use L-arginine with captopril, enalapril, losartan, valsartan, diltiazem, amlodipine, hydrochlorothiazide or furosemide.
Certain nitrate-based drugs are used as treatments for cardiovascular disease. These include nitroglycerin and a similar drug known as isosorbide. People using nitrate medications can not safely take L-arginine supplements. The National Institutes of Health notes that the combination of L-arginine and nitrates can cause excessive blood flow to the heart, leading to dizziness and lightheadedness.
The prescription drug sildenafil, an erectile disfunction drug, can lower blood pressure. Because L-arginine can also lower blood pressure, it's possible that the combination of products could lead to a drastic or sudden drop. This could cause discomforts such as dizziness, vertigo or lightheadedness. Although the National Institutes of Health regards this as a "moderate" interaction, advising caution rather than outright avoidance of the combination, you should not us L-arginine and sildenafil together without first consulting your physician.
The Mayo Clinic urges patients using anticoagulants, or blood thinners, to consult a licensed practitioner before using L-arginine supplements. These powerful drugs interact with many drugs, herbs and supplements, possibly incuding L-arginine. They Mayo Clinic notes that L-arginine could increase bleeding risk associated with these drugs, leading to nosebleeds, excessive bruising or hemorrhage. Powerful blood thinners include warfarin, while products with similar but weaker effects include common pain-relieving drugs such as ibuprofen and aspirin.