Levocarnitine

What it is

Levocarnitine is the natural form of carnitine, a molecule that shuttles long-chain fatty acids across the mitochondrial membrane so they can be burned for energy. The body makes it from lysine and methionine and also obtains it from meat and dairy. As an over-the-counter supplement it is taken for fatigue and general energy support.

Used for

• Energy

What to know while taking it

It is typically taken with or after food, which is better tolerated; the dose range on the shelf is wide because needs differ between people. Only the levo form should be used, as the D-isomer found in some older racemic products interferes with carnitine's own action. Gut bacteria convert part of an oral dose into compounds that can produce a noticeable fishy odour of the breath, sweat or urine, which is harmless but is the most common reason people stop.

When to see a doctor

Persistent nausea, diarrhoea or an odour that does not settle is worth raising with a doctor, who may want to check whether supplementation is needed at all. Anyone with kidney impairment or on dialysis should have carnitine use supervised rather than self-directed.

Worth knowing

• Can give a fishy body odour