Undeclared substances in sports supplements: what a 2026 systematic review actually found

Systematic review of undeclared prohibited substances and pharmacological adulterants in dietary supplements: prevalence, detection, and risks in sport. Frontiers in Sports and Active Living, 2026.

What's really in that bottle?

What the researchers set out to do

The researchers wanted to answer three questions:

1. Which banned or unapproved substances have actually been found in sports supplements?

2. Which product categories are they found in most often?

3. And which laboratory methods are being used to detect them?

   
   

This is a systematic review, meaning the authors didn't test any supplements themselves, they gathered and synthesised studies that had.

The method

The review followed PRISMA guidelines, the standard framework for conducting systematic reviews transparently. Searches covered Scopus, Web of Science and SPORTDiscus, screening 12,031 records down to 46 studies that met the inclusion criteria. Included studies were original empirical research published in English between 2010 and 2025 that had analytically tested supplements for undeclared substances. Studies about athlete behaviour or supplement use patterns were excluded, this review is only about what was found in the products themselves. Two reviewers extracted the data independently, with a Kappa coefficient of 0.753 which indicated substantial agreement between them.

On closer inspection

What the researchers found

Stimulants were the most commonly reported contaminant class, appearing in 21 of the reviewed studies. These included amphetamine derivatives such as DMAA and octodrine, phenethylamine analogues including oxilofrine and hordenine, and appetite suppressants such as sibutramine and phentermine which histrocially have been withdrawn from several markets over cardiovascular concerns.

Anabolic-androgenic steroids came second, reported in 11 studies. Substances detected included stanozolol, nandrolone, trenbolone, oxandrolone and DHEA.

SARMs (selective androgen receptor modulators) appeared in five studies — ostarine, ligandrol, RAD-140 and others. These are compounds developed pharmaceutically but never approved for human use anywhere. Also detected: beta-2 agonists (higenamine, in six studies), diuretics and masking agents (six studies), peptide hormones including MK-677 (two studies), beta-blockers, and the glucocorticoid dexamethasone.

By product category, sports and general performance supplements such as pre-workouts and energy products, were the most frequently implicated (14 studies), followed by steroid-based and hormonal products (11 studies) and weight-loss supplements (10 studies). Protein and muscle-building products appeared in four studies.

One finding deserves attention. Herbal and traditional supplements were implicated less often (three studies), but when they were adulterated, they tended to contain potent synthetic stimulants concealed behind plant-derived names such as methylhexanamine presented ( ageranium extract being the recurring example). The authors note this may pose a greater risk precisely because consumers may assume "natural" means safe.

What it doesn't say

The review does not establish a contamination rate. It counted how many studies reported each substance class, not what proportion of supplements on the market are affected. A widely quoted figure of 9–15% appears in the paper's introduction, cited from earlier literature. It is not a finding of this review.

The included studies are heterogeneous. Different designs, different sampling methods, different products. The authors state plainly that this limits direct comparability.

Sampling was not random. Many of the underlying studies deliberately tested products already suspected of adulteration, which inflates apparent prevalence. That is appropriate for detection research and inappropriate for estimating how common the problem is.

The geography is uneven. Evidence is concentrated in the Americas, Asia-Pacific and Europe. Research from the Middle East, North Africa and South Asia is largely absent, so the authors note that global prevalence may be underestimated.

The Empowering Nutrition take

The finding here isn't "supplements are dangerous." It's narrower and more useful: the products most likely to contain something undeclared are the ones sold on the promise of a rapid effect. Pre-workouts, fat burners, anything marketed around hormones or muscle gain.

That is a coherent pattern rather than random contamination. Products promising a dramatic result are the products most likely to have had something added to deliver it.

The practical implication is not to avoid supplements, it is to recognise that the risk is not evenly distributed, and to treat third-party testing as essential rather than optional in exactly those categories. In the UK, Informed Sport is the relevant certification scheme, batch testing rather than a single approval, which matters because contamination is often a batch-level problem.

For anyone competing under anti-doping rules, strict liability applies. An athlete is responsible for what is in their body regardless of how it arrived there. Strict liability makes sense for an adult professional. It sits less comfortably when the athlete is fifteen, buying a product a teammate recommended, with a parent paying for it. Legally the responsibility still rests with them, but practically, it's shared. Coaches, parents and support staff are the people with the time, the scepticism and the internet access to check a batch number. This should not a burden on the athlete's team, it's the most efficient place for the check to happen, because it only has to happen once.