Do arginine and nitric oxide boosters actually help your workout?

Short answer

Arginine doesn't work. Blood flow, nitric oxide, reps and max weight all stayed the same. Citrulline (6-8 g) has a small effect, about 3 more reps out of 51.

Do arginine and nitric oxide boosters actually help your workout?
'Arginine → more nitric oxide → more blood flow → better workout' — does this hold?
Arginine is a staple in pre-workout supplements, sold as a way to raise nitric oxide, which widens blood vessels, for a bigger pump and more strength. We checked this formula one step at a time.
Swallowed arginine barely reaches the blood
The gut breaks much of it down first
A lot of the arginine you swallow is broken down in the gut. In a trial where 20 people took several doses of arginine or citrulline for 1 week, blood arginine actually rose more with citrulline. Citrulline is absorbed well and then turned into arginine inside the body.
More arginine in the blood, same blood flow
24 people, 7 days, 12 g a day
24 people took 12 g a day of an arginine booster or a dummy pill for 7 days, then did an arm workout. Blood arginine rose with the booster, but blood flow, heart rate and nitric oxide by-products were the same as with the dummy pill. The extra blood flow came from the exercise itself.
What about actual performance?
Same reps, same max weight
16 people took arginine (3.2-9.6 g a day) or a dummy pill for 4 days and did arm sets to failure: reps and blood nitric oxide were the same (2025). Another 16 people took 3 g of an arginine booster 45 minutes before lifting: their max bench press, max leg press and reps matched the dummy pill.
The analysis that found big effects had math errors
3 studies inflated the result
A 2020 analysis that pooled 18 studies claimed arginine strongly boosts endurance. In 2025 another researcher found 3 studies with effect values of 3.25 to 5.23, far off the chart, caused by entering error values the wrong way. Removing those 3 changed the result dramatically.
Citrulline is a bit different
About 3 more reps out of 51
An analysis of 8 studies with 137 people found that 6-8 g of citrulline malate taken 40-60 minutes before training added 3 reps (6.4%) to an average of 51 reps at 70% of max. Another analysis of 4 studies found no gain in max strength. Citrulline-rich foods like watermelon did not change endurance.
The latest analysis: still a small effect
30 trials, 644 people
A 2026 analysis of 30 trials with 644 people found citrulline malate gave a small lift in performance but did not make exercise feel easier. A 2019 analysis of 12 studies with 198 people found the same. In both, the gap from the dummy pill was small.
Bottom line: arginine boosters don't work
Citrulline adds a few reps at most
With arginine, blood flow, nitric oxide, reps and max weight all stayed the same. Taking 6-8 g of citrulline malate 40-60 minutes before training adds a few reps, but max strength stays the same. Muscle and strength still come down to training volume and diet.