Every longtime lifter’s bathroom cabinet has its boneyard. Under the sink, you’ll find a few bottles of once-promising ingredients that were hyped by a study or two years ago, but nothing in the last decade. (Looking at you, arachidonic acid.)

But look in that lifter’s gym bag or medicine cabinet, and you’ll find a different lineup: the supplements that have continued to establish their bona fides in the lab, as well as backing them up in the weight room.

The following five ingredients should be considered for any new formulation positioned to help athletes get bigger, stronger or more powerful.

A note: Two big names you won’t find here: protein and caffeine. Why? Protein intake is so fundamental to muscle growth, to call it an “ingredient” is an understatement. And caffeine tolerance is highly individual, whereas the ingredients below can be considered more universal.

Creatine monohydrate

Every year dozens of new creatine studies come out, and the pile of research backing the legitimacy of this compound keeps growing. One of the latest additions is a recent meta-analysis co-authored by some big names in sports supplement research, which concluded that taking creatine “promotes a small increase” in muscle mass for both the upper and lower body across numerous populations–men and women, older and younger.

But here’s something that doesn’t get discussed often enough: creatine’s potential to lessen the impact of less-than-optimal protein intake.

“Normally I get plenty of protein, but there are days that maybe I don't eat as much,” explained researcher Abby Smith-Ryan, Ph.D., co-author of numerous creatine-related studies. “Women in particular also tend to undereat, and creatine could be one of those ‘first lines of defense’ to help them in particular. That 5-gram daily dose can be really helpful because of people’s inconsistency.”

Beta-alanine

The nonessential amino acid beta-alanine has become a near-mandatory inclusion in every pre-workout workout blend–which is a bit odd, since there’s no research to date showing that taking it at a specific time, or in a single dose, offers any particular benefit.

However, when taken consistently for weeks at a time, beta-alanine has been shown to help increase max strength and decrease athletes’ perceptions of fatigue while training. For lifters following high-intensity training programs, it has also helped to boost lean muscle mass and improve overall body composition. A major reason for these benefits is that beta-alanine raises blood levels of the powerful lactate buffer carnosine, allowing athletes to do more work—and work harder—before “the burn” makes them quit.

Some rumblings in recent years suggest that beta-alanine may have nootropic potential as well, but don’t hold your breath. Its mental benefits appear to be limited to very specific populations, like adults experiencing cognitive decline.

Beetroot and/or citrulline malate

These two popular ingredients come from different sources, but supplement researcher Krissy Kendall, Ph.D., groups them together into a category of “nitrate-boosting ingredients.”

“Both of them increase nitric oxide (NO) production, which increases blood flow and nutrient delivery,” she explained. “And a great thing is that unlike creatine and beta-alanine, both also work acutely. So you can take them just 30-60 minutes before your workout and see benefits.”

While the timeline they do it on is different, NO-boosters and beta-alanine both help lifters add muscle by delaying fatigue and creating better training sessions. Line up a few months of better workouts, and you can expect better results.

Given how they work, Kendall said NO-boosters are a natural pairing with the ultimate acute performance-booster, caffeine. “On their own, citrulline malate and beetroot extract have been shown to improve performance,” she stated. “Citrulline malate has been shown to increase training volume in the weight room, while beetroot has been shown to improve endurance performance. Couple those with caffeine, which stimulates the central nervous system (CNS) and reduces perceived fatigue, and you're sure to have a winner.”

Magnesium

While the ingredient list on muscle-building supplement blends can be long, the number of ingredients with current, substantial research backing them is actually pretty short.

But if you expand to include supplements that can indirectly help muscle growth by boosting recovery, the room gets a little bigger. The reasoning is simple, according to Kendall: “If you recover faster, you have more opportunity to train and grow.”

That’s where magnesium can shine. In the very short term, this elemental electrolyte helps to block calcium during muscle contractions, helping muscles to relax after exertion. Stretch out the timeline a little, and an August 2022 study in the Journal of Strength and Conditioning Research showed that 10 days of magnesium supplementation significantly reduced muscle soreness, perceived exertion and perceived recovery, helping young subjects recover from lifting and perform after 48 hours of recovery.

Supplementing with magnesium can even translate to increased testosterone levels in men with low magnesium levels–one possible explanation for the longtime popularity of ZMA (zinc, magnesium aspartate and vitamin B6) supplements among bodybuilders. Magnesium also made the headlines during Covid-19, since it plays a crucial role in synthesizing and activating vitamin D, and vitamin D deficiencies carry the risk of muscle atrophy, weakness and decreased protein synthesis.

Magnesium is pretty easy to get from a balanced diet, but more than half of adults don’t meet the recommended daily intake, making a compelling argument for supplementing.

Omega-3 fatty acids

Omega-3 fatty acid sources like fish oil, flax oil and krill oil make enough headlines for their cardiovascular and cognitive benefits to make them worth considering for everyone–not just athletes. But a growing body of research indicates they may have anabolic potential as well.

“EPA [eicosapentaenoic acid] and DHA [docosahexaenoic acid] aren’t always in the conversation about muscle-building because they are lipids and not proteins. Fatty acids won’t necessarily have a role in the muscle-building process in the typical sense of ‘building blocks’ like amino acids,” explained Kaitlin Roke, Ph.D., director of scientific communication and outreach at the Global Organization for EPA and DHA Omega-3s (GOED). “However, EPA and DHA are found in almost every cell of the body, including muscle cells. EPA and DHA are an important part of the body’s inflammatory response; therefore, they are important ingredients to consider when targeting exercise and muscle recovery from exercise.”

Just how big of an impact can improved recovery actually have? Studies have shown that eight weeks of omega-3 supplementation boosted muscle protein synthesis (MPS) both in older people and healthy young populations. A more recent study in 2022 found significant increases in a wide range of strength and size measurements in older adults from taking krill oil for six months.

However, all of these benefits have been shown to be most pronounced when fatty acids are taken consistently for weeks or months straight, similar to creatine or beta-alanine. This could be because people simply aren’t getting these essential nutrients elsewhere.

“Generally, most people are consuming low to no EPA and DHA in their diet,” Roke said. “So thinking about how to get more can be important for overall health, but also for achieving specific health goals.”

Given that omega-3 fatty acids have also been repeatedly connected in research to improved workout recovery, decreased muscle soreness, and joint pain, their spot in the “stack” of discerning strength athletes is getting stronger by the day.

Nick Collias is a writer and editor with over a decade of experience working in the health and fitness industry. From 2016 to 2021, he was the host of the Bodybuilding.com Podcast, interviewing elite athletes and training thought-leaders on a wide range of exercise, nutrition and lifestyle topics. Additionally, he has worked for the last 20 years as a longform print and online journalist, as well as a book author, ghostwriter and editor.