Cocaine: general

Cocaine is a stimulant and local anaesthetic obtained from leaves of Erythroxylum coca [1][2]. It's a tropane alkaloid, C17H21NO4 [1][3]. Coca leaves have a long history of use in South America by chewing, going back millennia [2][4]. The purified drug was first isolated in the mid-1800s and went into tonics and Coca-Cola before being brought under international control in 1961 [2][4]. It exists as a hydrochloride salt (powder) or as free base (crack) [2]. It also has a narrow legitimate medical use as a local anaesthetic, mainly in ENT surgery, at defined concentrations [5].

The two things that matter most before anything else:

Stimulants as a class produce their overdose symptoms through excess norepinephrine and dopamine in the synaptic cleft [6]. In a stimulant overdose that excess can produce heightened alertness, dilated pupils, fast heart rate, high blood pressure, high body temperature, and seizures [6]. An overdose can lead to cardiovascular collapse, multiorgan failure, and death [6]. As with stimulants generally, what an overdose looks like varies person to person, depending on health conditions, the type of stimulant, dose, and route of administration [7].

Mixing raises this risk further. Sympathomimetic toxicity can come from one stimulant taken to excess or from multiple drugs used in combination [6]. Alcohol and other stimulants together are advised against for this reason [8].

If you're going to use it: stay hydrated, set up someone you can call if you start to feel panicked, and get help immediately for chest pain, seizure, or extreme agitation [8]. Guidance on recognising and responding to stimulant overdose includes the use of naloxone when opioids are also involved [9]. No medication reverses a stimulant overdose the way naloxone reverses an opioid one; acute symptoms are managed with medical treatment in a medical setting, not something to wait out at home [9].

References

1. Cocaine | C17H21NO4 | CID 446220 — PubChem, National Institutes of Health (NIH)
2. Cocaine: An Updated Overview on Chemistry, Detection, Biokinetics, and Pharmacotoxicological Aspects including Abuse Pattern – PMC — National Library of Medicine (NIH)
3. Cocaine | The Merck Index Online — Royal Society of Chemistry
4. Cocaine Toxicity — National Library of Medicine (StatPearls)
5. Cocaine use disorder: Epidemiology, clinical features, and diagnosis — UpToDate
6. Sympathomimetic Toxicity – StatPearls — NCBI Bookshelf
7. Stimulant Guide: Overdose Prevention and Response — Centers for Disease Control and Prevention
8. Harm reduction and methamphetamine use — NSW Health
9. SAMHSA Overdose Prevention and Response Toolkit — Substance Abuse and Mental Health Services Administration