How I decide whether a supplement is worth your money
Three questions, in order, and most things fail the second one. Including a few that sit in almost every cupboard I look at.
October 28, 2026 · 6min read · Rob Amoroso
Someone asks me about a supplement most weeks. Usually they have already bought it.
I am not against supplements. I am against paying for something because a podcast mentioned it. So here is the actual filter, in the order I apply it, and where some common ones land when I run them through it.
Question one: is it already in you, and is it in food?
The first thing I want to know is whether the thing exists in human biology already, and whether you could get it from eating.
Creatine is in red meat and fish, and your body makes it. Glycine is in skin, bone broth and collagen. Taurine is in shellfish. Betaine, which you will see sold as TMG, is in beets and spinach. These are not foreign compounds. They are things your body already handles, with machinery already built for them.
If something is not found in the body and not found in food, I start sceptical and the evidence has to be much better before I stop being sceptical.
I pay particular attention to anything conditionally essential. That means your body normally makes enough, but under certain conditions it cannot keep up. Illness, hard training, pregnancy, ageing, a genetic variant that slows one step down. Glycine and taurine both sit here. That gap between what you make and what you need is the most honest reason a supplement has to exist.
Question two: does the evidence actually support it
Here is where the first question stops being enough, and I want to be straight about that rather than pretend one test does all the work.
BCAAs pass question one and still do not work as sold. Branched-chain amino acids are in food and in you, and there is a plausible mechanism. But building muscle requires all nine essential amino acids, and giving you three of them produces a submaximal response. If you are eating enough protein, they are close to pointless. The mechanism story was good. The trials did not back it.
So everything gets sorted again, by how good the evidence actually is. I use three levels, and I use the same three when I write a summary for a client's doctor.
Well established. Replicated in decent human trials, with an effect size worth the money.
Plausible. A real mechanism and some human data, but thin, small, or not yet replicated. Worth trying in the right person. Not worth promising.
Exploratory. Interesting. Mostly animal work, or very small studies, or a condition that is itself still argued about. I will say so out loud rather than let the price tag imply more.
Here is that list sorted honestly.
Well established: Creatine monohydrate, by a distance. Hundreds of trials for strength and lean mass, cheap, and the one I recommend most. Melatonin for shifting your body clock, at low doses, where the timing matters more than the dose. L-citrulline for blood flow and exercise performance.
Plausible: Glycine for sleep quality, on a handful of small trials. Taurine, where most of the promising work is still in animals. TMG for homocysteine. CoQ10 and its ubiquinol form, which are well supported in mitochondrial disease and in statin-related muscle pain, and thin in healthy people. Methylated B vitamins, which matter in specific situations and are oversold as something everyone needs. ALCAR, where the human results are mixed. NAC, which is genuinely established for specific clinical uses and much weaker for general wellbeing. L-tryptophan. SAMe, which has reasonable data for mood and joint pain and comes with a warning below.
Exploratory: DAO enzyme, for histamine intolerance. The studies are small, and the condition itself is still argued about, so exploratory is the honest label for the research.
I will also tell you that I take it, and that I have had clients get obvious relief from it. That is experience, not evidence, and I am not going to dress the first thing up as the second. This is the part people usually get backwards: exploratory does not mean do not use it. It means I will not pretend the research is stronger than it is while you decide. Those are different claims and you are entitled to both of them.
Superseded: BCAAs, for the reason above.
Question three: is there a gap in this person
Even a well-established supplement is a waste of money if you did not need it.
So before anything goes in, I am looking at four things together: what someone actually eats, what their bloodwork says, what their genetics suggest, and what their stress and sleep look like. I am looking for a gap between what their body needs and what it is getting.
A word on the genetics, because this is where a lot of nonsense lives. A variant that slows one enzyme down is a hypothesis, not a prescription. It tells me where to look. It does not tell me what to do, and anyone selling you a supplement stack off a gene report alone is overreaching. I treat a gene finding exactly as I treat everything else: well established, plausible, or exploratory, and I say which.
Then, if we try something, we log it. What changed, what did not, how the person actually felt. One thing at a time, so we can tell what did what.
What logging everything is actually for
Most of my filtering happens before something goes in rather than after, so I do not pull things out often. But here is the one time I did.
A client was on blood pressure medication and taking L-citrulline. Well-established supplement, good reason to be taking it, no mistake made by anyone.
Then his blood pressure started dropping sharply after hard training sessions. Not dangerous, but a clear pattern, and it showed up in what he was logging week to week.
L-citrulline widens blood vessels. That is the entire point of it. His medication was doing the same job. Stack them, add the vasodilation that comes with hard exercise, and you get a bigger drop than any of the three would produce alone.
So we took the citrulline out. Not because it was bad, but because we needed to know which of the two was doing what. I told his doctor what we were seeing. His doctor halved the blood pressure medication, which was a medical decision and his to make. Once that settled, we reintroduced the citrulline at a smaller dose, and he has had no problems since.
That is what the logging is for. His doctor sees him every few months. I was looking at his training and his numbers every week. Nobody did anything wrong, and the interaction was only visible to whoever was watching closely enough, often enough.
Two safety notes, since I have named them
SAMe interacts with SSRI and SNRI antidepressants, with a real risk of serotonin syndrome, and it can trigger mania in people with bipolar disorder. Do not start it on your own if you take anything for your mood.
L-citrulline, and anything else that widens blood vessels, deserves a conversation with your prescriber if you are on blood pressure medication, for the reasons above.
I am a coach, not a clinician. I do not prescribe, I do not adjust anybody's medication, and anything that needs a medical decision goes to the person qualified to make it. What I do is notice things between those appointments and make sure the right person hears about them.
The short version
Is it in you and in food. Does the evidence hold up. Do you personally have a gap.
Most things fail at the second question. A few fail at the third, which is a more expensive way to find out, because the supplement works fine and simply was not the thing you were missing.
And if nobody is writing down what happens after you start it, the whole exercise is guesswork with a receipt.