The best-evidenced sports supplement there is. Corrective for vegetarians, optional for everyone else.
TrustedSupp Tier System™ · Tier 4Take by choice, or not at all
Check before you startThis one has documented interactions with medication classes where the consequences are serious. If you take any prescription medicine, run it past a pharmacist before starting.
Evidence strength
95/100Very strong
WEAKLIMITEDMODERATESTRONGVERY STRONG
What the evidence supports: strength, power output, and lean mass gain — not the longevity claims sold alongside it.
This scores how well-supported the claim above is — not how much benefit you personally would get. A high score on a narrow claim does not extend to everything the product is marketed for.
How long to take it
Ongoing while training. Stores deplete over about a month after stopping.
Who it's actually for
Anyone doing resistance or high-intensity training; vegetarians, who start with genuinely lower stores; and increasingly studied in older adults for muscle retention.
Safe upper limit
Verified
No formal limit; 3–5 g daily is the standard dose
Extensively studied and safe in healthy people. Caution with existing kidney disease is precautionary rather than proven.
No toxicological UL exists. Health Canada's monograph instead sets permitted label doses: 3–5 g/day maintenance, or a supervised loading protocol up to 20 g/day short-term.