Who should not take L-citrulline?

No trial below identifies a group who should categorically avoid L-citrulline, since most of the research is in healthy adults over short periods. Reduced kidney function, blood-pressure medication, and a specific group of rare inherited metabolic disorders are the clearest reasons to check with a doctor first.

People with reduced kidney function

The kidneys are where the body converts circulating citrulline into arginine, and a 2008 dose-finding study found that at higher citrulline doses (10 g and 15 g), that conversion appeared to become saturated — plasma citrulline still rose, but arginine rose less than proportionally. That study was done in healthy men with normal kidney function; nobody has tested how reduced kidney function changes citrulline handling at a supplement dose. Given that the kidneys are the specific organ doing the relevant conversion work, ask a doctor before starting an L-citrulline supplement if you have diagnosed kidney disease.

People on blood pressure medication

L-citrulline has lowered blood pressure in adults who already have elevated blood pressure in several trials — see L-citrulline benefits: what the research does and doesn't show for the specifics. Combining that effect with a blood-pressure medication hasn't been tested, so ask a doctor before adding L-citrulline if you're being treated for high blood pressure, rather than assuming the two won't add up.

A rare inherited condition where citrulline is used medically — the opposite situation

Urea cycle disorders are a group of rare, usually inherited conditions in which the body can't properly process the nitrogen waste that the urea cycle — the same cycle citrulline is part of — is meant to handle. A 2013 pharmacology review lists urea cycle disorders among the conditions where citrulline supplementation is being explored, under medical supervision, specifically because of its role in that cycle. That's not a reason for a healthy person to start supplementing — it's the opposite situation, a diagnosed inherited condition managed by a specialist — but it's worth ruling out with a doctor if a family history of a urea cycle disorder applies to you, rather than guessing before adding any amino acid supplement on your own.

Pregnant or breastfeeding people, and children

We didn't find safety or dosing research on L-citrulline supplementation specifically in pregnancy, breastfeeding, or children. That's an absence of research, not a documented problem, but it's still a reason to ask a doctor before use in either case rather than assuming an amino-acid supplement is automatically fine.

Who this doesn't apply to

Outside the situations above, most of the research covered in L-citrulline benefits was done in healthy adults over periods of a single dose to six weeks; a couple of the blood-pressure trials specifically included mostly women. We haven't found research identifying a broader group of otherwise-healthy adults who should categorically avoid L-citrulline.

Questions people ask

Who should not take L-citrulline?

People with kidney disease and people on blood-pressure medication have the clearest reasons to check with a doctor first, given citrulline's role in the kidneys' arginine-conversion process and its blood-pressure-lowering effect in people who already have elevated blood pressure.

Is L-citrulline bad for kidneys?

No trial found evidence that it damages healthy kidneys at the doses tested. The kidneys are simply where citrulline gets converted into arginine, which is why reduced kidney function is a reason to ask a doctor first, rather than a documented harm.

Is L-citrulline safe for kidney disease?

This hasn't been tested in people with diagnosed kidney disease. Ask the doctor overseeing that diagnosis before adding L-citrulline.

Can pregnant women take L-citrulline?

There isn't enough safety data to say either way. Ask a doctor before using L-citrulline if you're pregnant or breastfeeding.