The supplement aisle promises a lot; the evidence backs very little of it. Here’s a practical, honest breakdown — what actually has research behind it, and what to watch out for regardless of which one you take.
The two with the strongest evidence
- Creatine monohydrate — one of the most studied supplements in sport science, with consistent evidence for improving high-intensity, short-duration performance (sprinting, lifting) and supporting muscle mass gains alongside resistance training.
- Caffeine — well-supported for improving endurance and perceived effort at moderate doses, though individual tolerance and sleep impact vary a lot.
Reasonable, more situational
- Protein powder — useful for conveniently hitting protein targets, but it’s a food substitute, not something with its own independent performance effect beyond what adequate protein intake provides.
- Vitamin D and calcium — worth supplementing if you’re actually low; see our dedicated vitamin D and calcium guides.
- Iron — helpful if you’re deficient (common in endurance athletes and menstruating women), but supplementing without a documented deficiency doesn’t help and can cause side effects.
Weak or absent evidence
Most “fat burners,” testosterone boosters, and proprietary recovery blends either lack quality research or have been tested and shown little to no effect beyond placebo. A flashy label and a research-sounding ingredient name aren’t the same as clinical evidence.
The bigger issue: quality control
Unlike medications, supplements aren’t reviewed by regulators for safety or accuracy of their label before hitting the shelf. Independent testing has repeatedly found products containing less (or more) of an ingredient than labeled, or contaminated with substances never listed at all — including, in some cases, substances banned in competitive sport. If you compete under an anti-doping code, this isn’t a minor technicality: see our guide to WADA and prohibited substances for why this matters and how to reduce your risk.
Third-party testing certifications (such as NSF Certified for Sport or Informed Sport) verify that a specific batch was tested for label accuracy and banned substances — look for these logos if you compete at a tested level.
This page is educational and general in nature and does not replace individualized nutrition advice — see our medical disclaimer.