Rule 1 Citrulline

L-citrulline's a straightforward ingredient once you know what it's been tested for. Here's the triage our naturopaths run.

A good fit if

• You're middle-aged or older and blood vessel health is the reason you're looking
• You want a clean single-ingredient powder where the label dose is the dose
• You're fine with a small, average effect rather than a guaranteed one

Check with us first if

• You take blood pressure medicine, nitrates or sildenafil-type medicines. No interaction studies exist, and citrulline acts on the same blood vessel signal.
• You're planning to take it with L-arginine, which lowered blood pressure much more in older adults than citrulline alone.
• You're stacking it with several other pre-workout ingredients before very long, hard sessions.

• L-citrulline (pure). Best known for: The label weight is the citrulline dose, and it's the form used in blood vessel trials. Absorption: Gets past the gut and liver breakdown that limits oral arginine, and raises blood arginine. Typical use: 3 g a day in blood vessel trials in older adults. 8 g a day over 6 weeks in one gym trial.
• Citrulline malate. Best known for: Citrulline bonded to malic acid, and the form in most gym trials. Absorption: Same pathway. A 6-week trial found no difference from L-citrulline in nitric oxide markers. Typical use: 6 to 8 g of powder before training, which is only about 4 to 5.3 g of citrulline.
• L-arginine. Best known for: The amino acid citrulline turns into. Absorption: Mostly broken down in the gut and liver when swallowed, so it's a poor way to raise blood arginine. Typical use: Only permitted in skin-applied listed medicines in Australia, not oral ones.
• Watermelon. Best known for: The best-known food source. Absorption: Not characterised in our sources. Typical use: Didn't improve artery widening in trials. It's food, not a measured dose.

Reference values. There's no NRV or RDI. Your body makes citrulline, so it isn't an essential nutrient.

Typical supplemental range. Blood vessel trials in middle-aged and older adults mostly gave 3 g of L-citrulline a day, taken daily for up to 12 weeks. Gym trials used about 5.3 g in a single dose before training, and 8 g a day over 6 weeks.

Upper level. An Australian listed medicine can't provide more than 6 g of citrulline a day. No scientific Upper Level has been set, because the safety data for amino acids like this one is too thin to define one.

Worth knowing. With L-citrulline, the grams on the label are the grams of citrulline, so there's no ratio to work out. The 8 g a day gym trial sits above the Australian 6 g cap, so a listed medicine can't give you that dose. Your needs depend on your age, diet and health circumstances. Talk to one of our naturopaths.

Food first, where the diet allows it.

• Watermelon: the richest known food source. A reliable amount per serve wasn't available in our sources

This list is the part of the page we will not shorten. If any of it applies to you, talk to one of our naturopaths or your doctor before starting.

• Blood pressure medicines, nitrates and PDE5 inhibitors such as sildenafil. No interaction study exists. Citrulline works through nitric oxide and lowered blood pressure in older adults, so an added effect is plausible. Refer to a doctor or pharmacist.
• Combined with L-arginine. The pair lowered systolic blood pressure by about 10 mmHg in older adults, far more than either alone. Flag for anyone on blood pressure medicine.
• Pregnancy. Only trialled under specialist supervision for specific conditions. No general safety conclusion can be drawn. Don't recommend.
• Breastfeeding. No data at all. Don't recommend.
• Children and teenagers. Only studied in hospital and disease settings. Adult doses are unstudied.
• Heavy stacks with extreme training. One case of exertional rhabdomyolysis on a multi-ingredient stack including 10 g citrulline malate. Not attributed to citrulline.
• Dose. An Australian listed medicine can't exceed 6 g of citrulline a day, and no scientific Upper Level exists.