Pseudoephrine

For best safety practice, don't mix this drug with other stimulants.

Why: vasoconstriction, heart rate and blood pressure. PsychonautWiki says:

• “... may be dangerous to combine with other stimulants ... as they can increase one's heart rate and blood pressure to dangerous levels.” (PsychonautWiki, dangerous interactions table, "Stimulants" row, revision 148925)
• “Vasoconstriction can be described as a narrowing of the veins and blood vessels which results from a contraction of their muscular wall.” (PsychonautWiki, Vasoconstriction, revision 170337)
• “... it can also occur under the influence of traditional stimulants such as methamphetamine, caffeine, and MDMA.” (PsychonautWiki, Vasoconstriction, revision 170337)
• “Increased blood pressure is most commonly induced under the influence of heavy dosages of vasoconstricting compounds, such as traditional stimulants and stimulating psychedelics.” (PsychonautWiki, Increased blood pressure, revision 152273)