Research interaction map
What should not be mixed?
No pair in this library has a well-established universal “never combine” rule for healthy adults. The cards below separate timing conflicts, uncertain efficacy interactions and dose-dependent cautions.
The library lists reviewed pair-specific signals and keeps ingredient-level medication and condition cautions inside each guide. Only pairs with a specific, supportable signal are shown here. An unlisted pair means no established pair-specific interaction was identified in this review—not proof that every dose, product or person is safe.
Possible efficacy conflict during chronic co-useSystematic review
The combination is not proven to cancel creatine. A systematic review found mixed results: acute caffeine after creatine loading generally did not block caffeine's benefit, while chronic caffeine during loading interfered with creatine outcomes in some—but not all—studies.
Practical actionNo blanket avoidance rule is supported. If loading creatine, consider taking caffeine separately or reducing chronic high caffeine when gastrointestinal symptoms or a weaker training response is a concern.
Opposing circadian signals and altered melatonin exposureDirect human evidence
Evening caffeine can delay the body's melatonin rhythm. In a small pharmacokinetic study using high doses, caffeine also substantially increased exposure to an oral melatonin dose.
Practical actionDo not use melatonin simply to counter late caffeine. Keep caffeine away from the intended sleep window and review timing with a clinician for shift work or jet-lag protocols.
Potentially additive stimulationDirect human evidence
Human performance studies have combined caffeine and Rhodiola without showing that one cancels the other, and some reported additive performance effects. These studies do not establish long-term safety for people sensitive to stimulation.
Practical actionUse earlier in the day and monitor anxiety, agitation, heart rate and sleep. Extra caution is appropriate with cardiovascular conditions or stimulant medication.
Overlapping nitric-oxide and blood-pressure effectsDirect human evidence
The ingredients act through related nitric-oxide pathways. Small human trials have used them together without showing cancellation, but both can influence vascular tone and blood pressure.
Practical actionMonitor light-headedness and blood pressure. Seek professional review with low blood pressure, antihypertensives, prescription nitrates or PDE5 inhibitors.
Mineral absorption at very high zinc intakeOfficial safety guidance
NIH notes that 142 mg/day of supplemental zinc interfered with magnesium absorption in one study. That zinc amount is far above Dose Radar's 10–25 mg research range.
Practical actionRoutine researched amounts do not create an automatic separation rule. Review the stack if zinc intake is unusually high or used long term.
Mineral absorption at very high zinc intakeOfficial safety guidance
The magnesium in bisglycinate still contributes to total elemental magnesium. NIH notes that 142 mg/day of supplemental zinc interfered with magnesium absorption in one study—far above Dose Radar's usual zinc range.
Practical actionRoutine researched amounts do not create an automatic separation rule. Total magnesium from all forms and unusually high or long-term zinc intake should be reviewed.
Mineral absorption at very high zinc intakeOfficial safety guidance
The magnesium in L-threonate still contributes to total elemental magnesium. NIH notes that 142 mg/day of supplemental zinc interfered with magnesium absorption in one study—far above Dose Radar's usual zinc range.
Practical actionRoutine researched amounts do not create an automatic separation rule. Total magnesium from all forms and unusually high or long-term zinc intake should be reviewed.
Potentially additive sleepinessDirect human evidence
Both can promote sleepiness. One 2025 randomized trial used 3 mg melatonin with 600 mg/day ashwagandha for eight weeks and reported no clinically significant difference in adverse events, but one trial cannot establish safety for every user or extract.
Practical actionMonitor next-day drowsiness and do not drive after taking the combination. Review it with a clinician when using sedatives or when liver or thyroid concerns apply.
Psyllium and oral productsCheck timing
Psyllium forms a gel that can change how some oral products are absorbed. Official product labeling specifically requires separation from oral drugs; evidence for individual supplements is ingredient-specific.
Practical actionFollow each label and ask a pharmacist when medication is involved. Do not assume every supplement requires the same interval.
This screening covers supplements in the Dose Radar library only. Medications, diagnoses, pregnancy, surgery and product-specific blends can materially change the answer. Speak with a pharmacist or healthcare professional when appropriate.
