Guide
Is it safe to take L-citrulline every day?
For most healthy adults, yes, at the amounts trials have tested: no side effects at single doses up to 15 g, and no reported safety signal across a month at 1.5 g/day or 6 weeks at 8-12 g/day. No trial has tested daily use beyond 6 weeks.
Yes, for most healthy adults, at the amounts research has actually tested. A 2008 dose-escalation study found no side effects at single doses up to 15 g, a 2011 trial ran 1.5 g/day for a month with no adverse events, and a 2025 trial ran 8-12 g/day for 6 weeks with no safety signal reported. No trial has run longer than 6 weeks of daily use.
What "safe" is actually based on here
L-citrulline isn't a nutrient with an established safe upper limit set by a health authority — there's no tolerable upper intake level the way there is for, say, vitamin D. What exists instead is a small set of human trials, and "safe daily" has to be answered against what those trials specifically tested, not against the ingredient in the abstract.
The single-dose data
A 2008 study gave 8 healthy men single oral doses of 2 g, 5 g, 10 g and 15 g of L-citrulline on separate days, with blood tracked for 8 hours afterward. None of the men reported side effects at any dose, including the highest, 15 g. At the top two doses, the rise in blood arginine was smaller than expected relative to the citrulline given — the researchers think the kidneys' conversion of citrulline into arginine becomes saturated at high doses, which is a reason to expect diminishing returns, not a toxicity finding.
The daily-use data
Two trials have tested L-citrulline taken every day rather than as a single dose. A 2011 trial had 24 men take 1.5 g/day for a month and reported no adverse events. A 2025 randomized, double-blind trial had 33 resistance-trained men take 8 g/day of plain L-citrulline or 12 g/day of citrulline DL-malate for 6 weeks, alongside a structured resistance-training program; it reported on performance and a nitric-oxide blood marker but didn't publish a separate tally of side effects or dropouts, which is an absence of reported data rather than a clean safety result at that higher dose. Six weeks is the longest daily-use period tested in a trial we found — there's no published data on daily use for months or years.
Why more isn't assumed to be better
The saturation effect the 2008 dose-finding study found — less arginine produced per gram of citrulline at 10 g and 15 g than at lower doses — is the practical reason higher daily doses aren't automatically better, on top of there being no safety data at those levels taken every day. Exercise-performance trials cluster around 6-8 g as a single dose or 8-12 g/day for ongoing use; nothing in the research supports taking meaningfully more than that on the theory that more citrulline means more effect.
Who has a more specific reason to check first
The kidneys are where citrulline gets converted to arginine, which is a reason for people with reduced kidney function to check with a doctor before daily use — see who should not take L-citrulline. Anyone on blood pressure medication or a PDE-5 inhibitor has a separate reason to ask first, covered in L-citrulline and medications: what to check.
Questions people ask
Is L-citrulline safe?
In the trials available — a single-dose safety study up to 15 g, a month of daily use at 1.5 g, and 6 weeks of daily use at 8-12 g — nothing has turned up a specific safety signal. None of these trials is large, and none ran past 6 weeks.
Can I take L-citrulline every day?
The two trials that tested daily use — a month at 1.5 g/day and 6 weeks at 8-12 g/day — didn't report a safety problem. That's the extent of the direct evidence on daily use; nothing has been tested beyond 6 weeks.
Are L-arginine and L-citrulline safe?
The dose-escalation study behind most of this page tested L-citrulline alone, not combined with L-arginine. We didn't find a trial testing that specific combination for safety.
Are L-citrulline supplements safe?
At the doses and durations trials have tested — up to 15 g as a single dose, and up to 12 g/day for 6 weeks — the available data hasn't found a safety problem in healthy adults. That's a narrower statement than "safe," since it only covers what's actually been studied.
Is L-citrulline safe for kidneys?
No trial has tested L-citrulline specifically in people with reduced kidney function. Since the kidneys do the work of converting citrulline into arginine, and that conversion appears to saturate at high doses in healthy adults, this is a group with a clearer reason than most to check with a doctor first — see who should not take L-citrulline.
When to talk to a doctor
L-citrulline is a supplement, not a treatment for any condition, and none of the safety data above substitutes for a doctor's judgment about your own situation. Check with a doctor before daily use if you have reduced kidney function, take blood pressure medication or a PDE-5 inhibitor, or are pregnant or breastfeeding — and stop and check with a doctor if a new or unexplained symptom shows up after starting.
Related reading: how much L-citrulline should you take a day?, L-citrulline side effects, and who should not take L-citrulline.
Sources
- Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study A 2008 dose-escalation study gave 8 healthy men single oral doses of citrulline from 2 g up to 15 g and found no side effects at any dose, but at the two highest doses the expected rise in blood arginine was smaller than predicted — the researchers think the kidneys' conversion of citrulline into arginine becomes saturated at higher doses.
- Changes in resistance training performance, rating of perceived exertion, and blood biomarkers after six weeks of supplementation with L-citrulline vs. L-citrulline DL-malate in resistance-trained men: a double-blind placebo-controlled trial A 2025 six-week trial in 33 resistance-trained men found that daily L-citrulline (8 g) or citrulline malate (12 g) improved upper-body muscular endurance more than placebo and raised a blood marker of nitric-oxide production, with no meaningful difference between the two citrulline forms on any measured outcome.
- Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction A 2011 single-blind trial in 24 men with mild erectile dysfunction found that 1.5 g/day of L-citrulline for a month improved erection hardness in half the men, versus about 8% during a placebo month, with no adverse events reported — the study's own authors describe it as less effective than standard PDE-5 inhibitor medication.
- Citrulline: pharmacological perspectives and its role as an emerging biomarker in future A 2013 pharmacology review describes L-citrulline as a naturally occurring amino acid and urea-cycle intermediate that the body converts to arginine more efficiently than arginine converts to itself, and lists the range of conditions where its supplementation is being researched, from erectile dysfunction to rare urea cycle disorders.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.