Citrulline is used by some people to combat brain fog, improve energy levels, and enhance physical performance. But what does the science say about its effectiveness for these purposes?
This nootropic has no healthy human placebo-controlled studies that meet our inclusion criteria. Negative side effects can occur if used carelessly, so make sure you’re aware of the risks of Citrulline.
Read about the effects of Citrulline in relation to the amount of evidence we've found
Can citrulline help with brain fog?
The best evidence available is a group of anecdotal reports of people having both negative and positive results from the use of citrulline to deal with brain fog.
A third person said they tried citrulline for 4 weeks and experienced no relief from their brain fog.
Another person said it helped him with brain fog:
"My brain fog is nearly gone after supplementing with L-Citrulline 2000mg per day" 
One reason for brain fog can be a lack of cerebral blood flow. Citrulline appears to enhance cerebral blood flow. However, there's a need for more research on citrulline's potential to help with brain fog in otherwise healthy humans.
Can citrulline enhance your memory?
Citrulline had a protective effect on cerebrovascular functioning in a mouse model. It improved memory function after it had been destroyed by experimentally induced lack of blood (and therewith oxygen) supply to the brain. 
The study found that citrulline prevents neuronal cell death.
A compound's ability to bring cognitive performance back to baseline from an impaired state is a promising sign that it might help enhance cognitive performance in healthy animals or people. However, it has to be tested in healthy people to determine if it is actually effective, since it may very well not have any cognitive-enhancing effects in healthy individuals. Such tests have not been conducted in any studies on citrulline, so it is too early to state anything with confidence about its potential memory-enhancing effects.
Can citrulline improve your spatial memory?
No research in humans has examined the effects of citrulline for spatial memory.
In a mice study, citrulline was found at higher levels in brain areas involved in spatial memory and planning when those had likely been more activated.
"There were significantly [...] increased L-citrulline concentrations in the dentate gyrus (DG) and prefrontal cortex in the T-maze training group relative to the control one.” 
Another study found increased levels in rat hippocampi during memory retrieval. 
This is interesting evidence that citrulline is in some way possibly involved in spatial memory, but far from evidence that supplementing citrulline would lead to spatial memory enhancement.
Can citrulline enhance physical performance?
A meta-analysis on the acute effects of citrulline on high-intensity strength and power performance found an overall small beneficial effect. 
The legality and side effects of Citrulline
Frequently asked questions about Citrulline
Studies conducted on the effects of Citrulline in healthy humans
Last updated Saturday, June 10, 2023