Short answer: They work differently. Beta-alanine builds up in muscle over weeks and helped most in hard efforts lasting roughly 1 to 10 minutes; it often causes harmless tingling.12 Citrulline is taken before exercise; a meta-analysis found a small boost to strength and sprint work3 and none for endurance.4 Only one small trial tested both, and both beat placebo.5
| Beta-alanine | Citrulline | |
|---|---|---|
| How it is thought to work | Raises muscle carnosine, which buffers acid during hard effort2 | About 80% is turned into arginine, which the body uses to make nitric oxide, a blood vessel widener2 |
| How it was taken in studies | Daily for weeks: 84 to 414 g in total over 28 to 90 days2 | A single dose of at least 3 g, 30 minutes or more before exercise3 |
| Pooled results | Small overall effect across 40 trials and 1,461 people; larger for exercise capacity over 30 seconds to 10 minutes1 | Small effect on strength and sprints across 12 studies and 198 people3 |
| Endurance | Little or no benefit for efforts over 10 minutes2 | No effect in 9 studies of 158 people4 |
| Side effects | Tingling in the face, neck and hands at 800 mg or more per dose, lasting 60 to 90 minutes, not harmful; itchy skin2 | Stomach discomfort2 |
| Safety data | 1.6 to 6.4 g a day for up to 8 weeks; none beyond 1 year2 | Up to 9 g for 1 day or 6 g a day for 16 days2 |
A 2017 meta-analysis of 40 placebo-controlled studies found a small overall benefit. Effects were larger for tests of how long people could keep going (capacity) lasting 30 seconds to 10 minutes than for timed performance, and training status did not matter.1 An earlier meta-analysis found a median gain of 2.85%, with benefit for efforts over 60 seconds and none for those under 60 seconds.6 NIH says results in competitive events are inconsistent and there is no expert consensus on its value.2
A 2019 meta-analysis of 12 studies found a small benefit for resistance sets and short sprints, with every single study's confidence interval crossing zero.3 A 2023 meta-analysis of 9 studies found no benefit for endurance.4 Most studies used citrulline malate, which is about 57% citrulline by weight, and NIH says there is little research support overall.2
In the one trial that tested both, 48 basketball players did 4 weeks of sprint training with 4.8 g of beta-alanine a day, 6 g of citrulline a day, creatine, all three, or placebo, with 8 people per group. All supplement groups improved more than placebo; the abstract does not say which single supplement did best.5
They suit different goals in the research: beta-alanine for repeated hard efforts of a few minutes after weeks of use, citrulline for a small single-session lift in strength or sprint work. Both effects are small. This is general information, not personal advice. More detail: the Beta-Alanine and L-Citrulline guides.