How long should I give something before deciding it does nothing? Magnesium and fish oil, six weeks in

Ran a proper stop trial on magnesium after four months because I could not tell whether it was doing anything. Kept a one line sleep note every morning for two weeks on, two weeks off, two weeks on, without telling my partner which phase I was in so I could ask her whether I had been snoring or restless. Result was a small but consistent difference in how long it took me to fall asleep and no difference in anything else. That was worth knowing, and it cost me six weeks and a notebook rather than another year of maybes.

Creatine is the useful counterexample because it has a clean, measurable, fast timeline: saturation takes a few weeks at a normal daily dose or about a week if you load, and the effect shows up as scale weight and as extra reps at the same load. That is what a supplement with a real, detectable effect looks like from the inside. If magnesium and fish oil worked like that for aches and sleep, you would already know at six weeks. Their case is weaker and slower, which does not mean zero, it means you need a better instrument than how you feel on a Tuesday.

Sort them by mechanism and the timelines stop being mysterious. Something that works acutely on a system, caffeine being the obvious one, tells you inside an hour. Something that has to build up in tissue takes as long as that tissue turns over, and omega threes are the classic case because they get incorporated into cell membranes and red cells live for months, so six weeks is genuinely early to judge. Something that is correcting a deficiency does nothing at all if you were not deficient, which is the case for most people taking most things. So the honest rule is: name the mechanism, and if you cannot, you cannot set a trial length and you are just buying reassurance.

One caution on running your own trials: pick one variable at a time and do not start two things in the same month, which is what you have done. If either of them had worked you would not know which. Also worth checking that whatever you are taking has enough of the active thing in it to matter, because dose ranges on shelves vary wildly and plenty of fish oil capsules are mostly filler by weight. For anything joint related that is not improving, a GP is the right stop before another three month order.

Six weeks is a fair trial for anything with an acute effect and far too short for anything membrane bound. Set a date, write down what would count as a change, and stop when the date arrives.