Drug Interactions
Every recorded combination, graded on one severity ladder from lethal to low, with the mechanism and the evidence behind each grade. Nexus is the data source.
Newer research chemicals and novel combinations may be missing. A pair that is not here has not been graded, and an ungraded pair is not a safe one. Check the sources at the foot of this page before you combine.
Select two or more substances and read every recorded interaction between them, graded on the ladder below, each with the evidence behind it.
interaction severity levels
These 5tiers are the site's whole severity vocabulary. The bar on a substance page, the facts label's interaction panel and the checker all grade on this ladder, worst first.
Fatal outcomes are documented for these combinations. Do not combine.
Serious harm documented: seizures, hyperthermia, cardiac or neurological injury.
A real interaction with variable or poorly characterised outcomes. Intensity and duration are unpredictable.
No dangerous interaction documented at typical doses. Standard precautions still apply.
The pair has not been graded. Absence of a grading is not evidence of safety.
No examples by definition: an ungraded pair is one nothing has been recorded for. Every surface labels it rather than dropping it, so a gap in the data reads as a gap.
dangerous mechanisms
Understanding why combinations are dangerous helps you recognize warning signs and respond appropriately.
Excess serotonergic activity causing a potentially fatal triad of symptoms.
Breathing slows to dangerous or fatal levels. The primary mechanism of opioid overdose deaths.
Combined stimulation of the cardiovascular system beyond safe limits.
Lowered seizure threshold or direct seizure induction from drug interactions.