Tongkat Ali and medications.

Tongkat Ali, also called Eurycoma longifolia or longjack, is an extract of the plant's root. It has been listed as a novel food, not yet authorised, since 2008, a position that still applies in Great Britain, so it should not be on sale here as a supplement, although you may still see it sold, and the duty to follow that rule sits with the seller, not with you. It is widely sold for testosterone support, libido and stress, and the evidence behind those claims is thinner than the marketing suggests. The one randomised placebo-controlled trial we cite ran for four weeks in 63 moderately stressed adults and reported lower salivary cortisol and improved mood scores. It measured no sexual function or libido outcome at all, so the libido claim does not rest on it. That trial was funded by the manufacturer of the extract it tested, was run by the first author's own company, and counts an employee of that manufacturer among its authors. The other commonly cited study did normalise testosterone in men with diagnosed low testosterone, but it was open label with no placebo group, so it cannot separate the supplement from expectation, and it studied men who were already deficient rather than men with normal levels. Two practical cautions stand out. Unregulated products have been found contaminated with heavy metals. There is also a single 2025 case report of new-onset atrial flutter in an older man after starting it, so anyone with arrhythmia, palpitations or unexplained dizziness should avoid it pending more evidence and flag any heart symptoms to a GP. It may also interact with immunosuppressants.