The problem with swallowing arginine
Arginine is the amino acid blood-vessel walls convert into nitric oxide, the molecule that tells vessels to relax. That part is textbook. The trouble is that enzymes in the gut wall and liver break arginine down before it can circulate, so a surprisingly small share of an oral dose ever reaches the blood. Researchers call this the arginine paradox.
How citrulline gets around it
L-citrulline, the amino acid watermelon is named for, is not handled by those same enzymes. Most of it passes into the blood, reaches the kidneys and is converted into arginine there. A 2016 trial in older adults found citrulline produced a larger and longer rise in blood arginine than the same amount of arginine itself.
Simplified pattern from published trials. Exact figures vary by study and dose.
Why not citrulline only, then?
Timing. Arginine that does survive the gut acts quickly. Citrulline needs to be converted first, so it is slower to rise but stays up longer. Together you get an early lift and a longer plateau. Memoclear goes a step further and lists two forms of each: base arginine plus arginine AKG for a slower release, and citrulline HCl plus citrulline malate, which adds a compound from the energy cycle.
What the amounts mean
Memoclear carries 400 mg of arginine forms and 200 mg of citrulline forms per capsule. Most blood-pressure and exercise trials use 3 to 6 g a day. So this is a daily maintenance amount, not a pre-workout hit, and the honest expectation is gradual support judged over weeks.
Who should be careful
Anything that raises nitric oxide relaxes vessels. If you take blood-pressure medicine, nitrates for angina or erectile dysfunction medicine, talk to your doctor before starting. People prone to cold sores sometimes find arginine sets them off.
The short version
Arginine is the ingredient everyone knows; citrulline is the one that gets arginine into your blood efficiently. Using both, fast and slow, is a sound design for a once-a-day capsule. Whether the amounts are enough for you is what the fair-trial guide is for.