Which supplements actually work?

Why most supplements disappoint

Walk into any supplement store and the wall of tubs, capsules, and powders implies you need a cabinet full of products to perform well. The evidence says otherwise. The International Society of Sports Nutrition (ISSN) publishes position stands — systematic reviews of the research — and their conclusion is consistent: the list of supplements with robust, replicated evidence behind them is short.

The supplement industry is large, profitable, and minimally regulated in most countries. Marketing claims don't require the level of evidence demanded by clinical medicine. A single small study — often manufacturer-funded — can launch a product. By the time independent researchers replicate (or fail to replicate) the finding, it's already on shelves with glowing endorsements.

This guide focuses on what the weight of independent, peer-reviewed evidence actually supports. It covers the supplements most commonly asked about by people training for hypertrophy and general fitness — not every compound in existence.

The short list with strong evidence

Three supplements have enough replicated, independent evidence to appear in multiple ISSN position stands and meta-analyses as genuinely useful for healthy adults who train.

• Creatine monohydrate. The most researched performance supplement in existence. The ISSN Position Stand on Creatine (Kreider et al., 2017) reviewed over 500 studies and concluded that creatine monohydrate is the most effective ergogenic nutritional supplement available for increasing high-intensity exercise capacity and lean body mass. It works by raising phosphocreatine stores in muscle, allowing faster ATP regeneration during short bursts of maximal effort. The effect size is modest but real and well-replicated: roughly 5–15% improvement in high-intensity exercise performance, and meaningful long-term lean mass gains combined with resistance training. Standard general guidance is a maintenance dose around 3–5 g per day — loading phases are optional, not required. The monohydrate form has the most evidence; fancier, pricier forms (ethyl ester, buffered, HCl) don't outperform it in head-to-head comparisons. See our detailed creatine guide for the full breakdown.
• Caffeine. One of the most studied ergogenic aids in sports science. The ISSN Position Stand on Caffeine (Guest et al., 2021) found strong evidence for performance benefits in endurance exercise and moderate evidence for strength and power output. It works primarily by blocking adenosine receptors, reducing perceived effort and fatigue. Effects are meaningful at doses of approximately 3–6 mg per kilogram of body weight, taken 30–60 minutes before training. Tolerance develops with regular use, which is why cycling caffeine intake — reducing it on rest days, for example — is sometimes recommended. The catch: coffee works as well as a dedicated supplement. You don't need to buy anything new.
• Vitamin D (if deficient). Vitamin D is a hormone precursor, not strictly a performance supplement, but deficiency is common — especially in people who spend most of their time indoors or live at northern latitudes — and genuine deficiency is associated with reduced muscle function, fatigue, and impaired immune response. The ISSN acknowledges that correcting deficiency through supplementation is warranted. The key word is deficiency: if your levels are already adequate, supplementing further doesn't produce additional performance benefits. The only way to know is a blood test. Dosing guidance should come from a healthcare provider based on your actual levels.

That's the honest short list — three items. Everything else below is context on why the list is so short.

The convenience case for protein powder

Protein powder deserves its own section because it sits in an unusual category: it's not a supplement in the pharmacological sense. It's a food — a processed, concentrated protein source — and the evidence behind dietary protein for muscle growth is extremely strong. The question isn't whether protein works; it's whether you need powder to hit your intake.

Current evidence-based recommendations for people training for hypertrophy typically land in the range of 1.6–2.2 g of protein per kilogram of body weight per day, though individual needs vary. For an 80 kg person, that's roughly 128–176 g of protein daily. Many people can hit that through whole foods — chicken, fish, eggs, legumes, dairy — without any supplement. If you can, there's no reason to buy protein powder.

Protein powder earns its place as a convenience tool when whole-food intake is hard to achieve — busy schedules, poor appetite post-training, travel, or cost constraints. A whey shake isn't magic; it's a fast, cheap, portable protein source. Whey has a high leucine content and a strong essential amino acid profile, and the post-exercise window evidence (while less decisive than once believed) does support having protein available around training sessions. Our full breakdown is in the daily protein intake guide.

What's overhyped or unsupported

The following categories are widely sold and marketed. They also appear frequently in the research literature — with largely unimpressive results for healthy adults who train and eat adequately.

• BCAAs (branched-chain amino acids). BCAAs — leucine, isoleucine, and valine — are sold as muscle-building and recovery supplements. The evidence for BCAAs as a standalone supplement in people who already eat adequate protein is weak. If your daily protein intake is sufficient, you're already getting BCAAs through your diet. The ISSN notes that total protein intake matters far more than the specific amino acid profile of a supplement. BCAAs don't outperform cheaper whey protein — or whole food — when total intake is matched.
• Pre-workouts beyond caffeine. Most pre-workout products contain caffeine — which does have evidence, as noted above — alongside a cluster of other ingredients at doses too low to produce meaningful effects, or ingredients with insufficient evidence regardless of dose. Beta-alanine has some evidence for buffering muscular fatigue during repeated high-intensity efforts, but the effect is modest and training-specific. Citrulline malate has limited evidence. The majority of the 'pump', 'focus', and 'energy blend' ingredients are unsupported at the doses used in commercial products.
• Fat burners and thermogenics. No over-the-counter product meaningfully accelerates fat loss beyond what a calorie deficit already achieves. Many thermogenics rely on caffeine for whatever stimulant effect they produce. The calorie deficit created by the supplement's price tag — by redirecting that money to better food — would likely outperform the supplement itself. See our calorie guide for muscle building for how energy balance actually drives body composition.
• Testosterone boosters. Products marketed as natural testosterone boosters — typically based on fenugreek, ashwagandha, zinc, or various proprietary blends — show little to no clinically meaningful effect on testosterone levels in healthy men with normal baseline levels. The evidence is either absent, unreplicated, or based on studies in men with documented deficiencies — a medical condition requiring medical management, not supplements.
• Glutamine. Long marketed as an essential recovery supplement, glutamine research in healthy athletes with adequate protein intakes hasn't supported the promised benefits. The body synthesises glutamine endogenously, and dietary protein provides abundant amounts. The ISSN doesn't recommend glutamine supplementation for performance or recovery in healthy, well-fed athletes.
• HMB (beta-hydroxy-beta-methylbutyrate). HMB showed early promise in initial studies (several of which had industry involvement), but more recent independent meta-analyses have found modest to negligible effects in trained individuals who already consume adequate protein and creatine.

This isn't an exhaustive list. New ingredients appear constantly, and the same pattern repeats: industry-funded or preliminary studies, heavy marketing, then a failure to replicate in independent research. Healthy scepticism toward any newly marketed ingredient is warranted until independent evidence accumulates.

Evidence strength at a glance

The table below summarises the evidence strength for commonly discussed supplements. 'Strong' means multiple independent, well-designed trials and systematic reviews support the claim. 'Moderate' means promising but not fully replicated evidence. 'Weak' means limited, low-quality, or industry-funded evidence only. 'None' means the claim isn't supported by the available literature.

Sources: ISSN Position Stands on Creatine (Kreider et al., 2017), Caffeine (Guest et al., 2021), Protein and Exercise (Stokes et al., 2018), and Nutrient Timing (Kerksick et al., 2017); Lanhers et al. systematic review on creatine and strength (2017); Lim et al. systematic review on BCAAs (2022).

Training, diet, and sleep still win

Even the supplements with the strongest evidence — creatine, caffeine — produce effects that are modest relative to training consistently, eating enough protein and total calories, and sleeping adequately. A rough hierarchy of what actually drives hypertrophy and performance looks like this.

• 1Progressive overload in training. Adding volume or intensity over time is the primary driver of muscle growth. No supplement replaces it. Tracking your lifts and ensuring progression is happening is the single highest-leverage thing you can do — which is why a tool like SammaGym that automates progression suggestions is more useful than most supplements.
• 2Total protein intake. Getting enough protein daily — roughly 1.6–2.2 g/kg depending on training status and goals — provides the raw material for muscle protein synthesis. See the daily protein intake guide for how to calculate your target.
• 3Total calorie intake. A meaningful caloric surplus supports muscle gain; a moderate deficit supports fat loss while preserving muscle. Neither happens without getting energy balance right. The calorie guide for muscle building covers this in detail.
• 4Sleep and recovery. Most muscle protein synthesis occurs during sleep. Chronic sleep restriction impairs the hormonal environment, increases perceived effort, reduces training quality, and slows recovery. No supplement compensates for consistently poor sleep.
• 5Creatine monohydrate. After the above four are in order, creatine is the one supplement with strong enough evidence to recommend broadly to people training for strength and hypertrophy.
• 6Caffeine. If you already consume caffeine regularly and enjoy training with it, the performance benefit is real. If you don't currently use caffeine, starting a supplement habit for marginal performance gains isn't an obvious trade given tolerance development and sleep-disruption risks.

Supplements occupy the narrow margin at the top of an already-optimised routine. If the fundamentals aren't in place, optimising supplements is the wrong priority. Once they are, the evidence-based short list above is where to focus — not on the hundreds of products with weak or no evidence.