Start with nitric oxide
Nitric oxide, or NO, is a tiny gas molecule that the lining of your blood vessels makes on demand. Its job is simple: it tells the muscle around the vessel to relax. Relaxed vessel, wider channel, more blood through. The brain uses about a fifth of your oxygen supply, all of it delivered by blood, so how well those vessels open matters for how well it works.
Arginine: the raw material
The body makes NO from L-Arginine. That part is not in dispute. The problem is delivery. When you swallow arginine, enzymes in the gut wall and liver break down a large share of it before it reaches the bloodstream. Studies suggest well under half of an oral dose gets through. So arginine works, but a lot of what you take never arrives.
Citrulline: the back door
L-Citrulline is the amino acid that watermelon is named after. It is not broken down by the same gut enzymes, so most of it reaches the blood, travels to the kidneys and is converted into arginine there. The result, shown in several trials, is that a dose of citrulline raises blood arginine more than the same dose of arginine does.
Simplified illustration of a pattern reported across published trials. Exact figures vary by study, dose and timing.
Why use both, then?
Timing. Arginine that survives the gut acts fast. Citrulline takes longer because it has to be converted first. Put them together and you get an early rise from arginine and a later, longer rise from citrulline. Memoclear goes one step further and uses two forms of each: base arginine plus slower-release Arginine AKG, and citrulline HCL plus citrulline malate, which adds a compound from the energy cycle.
What the amounts mean
Memoclear has 400 mg of arginine forms and 200 mg of citrulline forms per capsule. Most blood-pressure and exercise trials use 3 to 6 grams a day, so this is a maintenance-level daily dose, not a pre-workout hit. That is consistent with a once-a-day capsule you take for months, and it is why we tell people to judge it over weeks. If you want a large single dose, this is not that product.
Who should be careful
Anything that raises nitric oxide relaxes blood vessels. If you take blood pressure medicine, nitrates for chest pain or erectile dysfunction medicine, the effects can add together. Ask your doctor before starting. People with frequent cold sores sometimes find arginine triggers them.
The bottom line
Arginine is the ingredient everyone knows. Citrulline is the one that actually gets arginine into your blood efficiently. Using both, in fast and slow forms, is a sensible design for a daily capsule. Whether the amounts are enough to notice is the question only a fair trial answers, and the 90-day review explains how to run one.