The immediate effects of a cordrazine overdose
An overdose was an unsafe dosage of a drug that was higher than was usually prescribed.
In 2267, shortly after administering a life-saving dose of cordrazine to Hikaru Sulu, Doctor Leonard McCoy accidentally overdosed himself, causing a fit of paranoia in which he ran amok, beamed from the USS Enterprise to the Guardian of Forever's planet and jumped through the portal. He remained under the effects of the drug for several hours, before eventually sleeping it off. (TOS: "The City on the Edge of Forever")
In 2364, Mark Jameson overdosed on an anti-aging treatment from Cerberus II. (TNG: "Too Short A Season")