Tongkat ali (Eurycoma longifolia) and fadogia agrestis are the defining 'natty testosterone booster' stack of the past few years, their popularity traceable in large part to the Huberman Lab podcast, which discussed them together as testosterone-support supplements. The framing — a natural way to raise testosterone without drugs — resonates with lifters who want the effect of steroids or TRT without the label of a PED. But the two herbs are not on equal evidentiary footing.
Tongkat ali actually has human data. Multiple randomised controlled trials and a meta-analysis exist, standardised extracts are commonly dosed around 200–400 mg/day, and a 400 mg/day trial in athletes reported no adverse effect on liver-enzyme or kidney markers over six weeks. On liver safety specifically, NIH's LiverTox rates it 'possible rare cause of clinically apparent liver injury' and documents a single self-limited case of jaundice in a bodybuilder — with the important caveat that undisclosed anabolic-steroid use is a competing explanation in that population.
Fadogia agrestis is a different story. There are no published human studies; the evidence is a small cluster of rodent experiments, largely from one research group. The same body of animal work that reported a short-term testosterone rise also found testicular damage and disruption of liver and kidney membranes with longer (28-day) dosing. There is no established safe human dose and no long-term human safety data at all.
The reality behind the trend is asymmetric: one component of the viral stack has genuine human trials and a reasonable safety record at standard doses, while the other rests on animal data that includes organ-toxicity signals. 'Natural' is not a safety claim, and the absence of human studies for fadogia is not the same as evidence that it is safe — it is an absence of evidence in either direction.