Guide
When is the best time to take L-citrulline?
No study has directly compared morning-versus-evening or with-food-versus-without timing for L-citrulline. The clearest timing data comes from exercise-performance trials, which dosed citrulline at least 30 minutes before training as an inclusion criterion; daily, non-workout-specific timing hasn't been tested against alternatives.
No trial has directly compared morning versus evening use of L-citrulline for daily supplementation. What the research does show is a consistent pre-exercise timing window: the trials behind the exercise-performance research gave citrulline at least 30 minutes before training, not right beforehand or hours in advance.
What the exercise trials' protocols show
A 2019 meta-analysis of citrulline and high-intensity exercise specifically excluded any study that dosed citrulline less than 30 minutes before exercise testing — meaning every trial behind that pooled result gave citrulline at least half an hour beforehand. A 2010 trial tested a single 8 g dose of citrulline malate before a bench-press training session, though the published study doesn't specify the exact number of minutes used. Beyond that half-hour minimum, no trial has compared different pre-exercise timing windows against each other to find an optimum.
Daily use, not tied to a workout
A 2025 trial testing L-citrulline over 6 weeks had participants take their full daily dose (8 g of plain citrulline or 12 g of citrulline malate) once a day, without tying it to a specific clock time or splitting it around training sessions. That's the closest thing to guidance on daily, non-workout-specific timing available, and it reflects a single trial's protocol rather than a tested comparison of timing options.
With food or without
No trial has tested whether taking L-citrulline with or without food changes its effect. General supplement-taking practice applies here as much as anywhere: a capsule taken with food is a reasonable way to reduce stomach upset if it bothers you on an empty stomach, though the trial that reported stomach discomfort as a side effect used a single large 8 g dose regardless of food timing.
Does L-citrulline break a fast?
That depends on which definition of "fasting" is being used, and no research answers it directly for citrulline specifically. As an amino acid, it carries a small number of calories and can trigger some digestive and metabolic response, which is enough to break a strict calorie-free fast by some definitions; whether it meaningfully disrupts the intended purpose of an intermittent-fasting protocol is a more personal question that isn't settled by research either way.
Questions people ask
When should I take L-citrulline?
Exercise-performance trials dose it at least 30 minutes before training. For daily, non-exercise use, no specific timing has been tested against another.
Can I take L-citrulline before bed?
No trial has tested evening or before-bed timing specifically, so there's no research-backed answer either way.
Should I take L-citrulline before or after a workout?
Every exercise-performance trial in the research above dosed it before training, at least 30 minutes ahead — none tested taking it afterward instead.
What time should I take L-citrulline for ED?
The one relevant trial used a once-daily dose for a month without specifying a particular time of day; see L-citrulline benefits for what it found.
Should I split my L-citrulline dose across the day?
No trial has compared split dosing against a single daily amount. The chronic 6-week trial above had participants take their full daily amount at once.
Sources
- Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis A 2019 meta-analysis pooling 12 studies (198 people) found a small but statistically significant benefit of a single citrulline dose (at least 3 g, taken 30+ minutes before exercise) on high-intensity strength and power performance, though every individual study's own result could still have been due to chance.
- Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness A 2010 crossover trial in 41 men found a single 8 g dose of citrulline malate before a bench-press session increased the number of repetitions completed as the sets went on, and reduced next-day and two-day muscle soreness by about 40%, compared with placebo; about 15% of participants reported stomach discomfort.
- 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.
- 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.
*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.