An amino acid that converts to L-arginine in the body, supporting nitric oxide production and blood flow.
Quick answer: This ingredient has moderate evidence — several clinical trials support its role in nitric oxide production and blood flow, particularly for exercise performance and circulation, though results vary by dose and individual.
L-Citrulline is an amino acid that the body converts into L-arginine, a direct precursor to nitric oxide. Nitric oxide relaxes and widens blood vessels, which is why L-citrulline is commonly studied for circulation, exercise performance, and blood flow support. The strength of evidence behind it is currently classified as moderate — several clinical trials support these effects, though results vary by dose and individual response.
Here's where L-Citrulline shows up in our current formulas:
L-Citrulline is often formulated alongside other circulation-focused ingredients that support blood flow through complementary mechanisms:
Combining ingredients with different, complementary mechanisms is generally more useful than taking several ingredients that all do the same thing — it's worth checking a product's full ingredient list rather than judging it on one "hero" ingredient alone.
As with any supplement ingredient, individual response varies, and it's worth checking with a healthcare provider before starting L-Citrulline if you're pregnant, nursing, taking medication (especially blood pressure medication), or managing a health condition. For a full breakdown of dosage and side effects, see the related health goal guide below.
At studied doses, most people tolerate it well, though it's always worth checking with a healthcare provider, especially if combined with other supplements or blood pressure medication.
We classify evidence as Strong, Moderate, or Limited based on the quantity, size, and consistency of clinical research specifically studying this ingredient for this use. See our Editorial Policy for details.
L-Citrulline converts to L-Arginine in the body and is often better absorbed orally, which is why many circulation formulas use citrulline instead of (or alongside) direct arginine.