The initial symptoms are mainly due to stimulatory effects and include nausea and vomiting, excessive salivation, abdominal pain, pallor, sweating, hypertension, tachycardia, ataxia, tremor, headache, dizziness, muscle fasciculations, and seizures.

[4] After the initial stimulatory phase, a later period of depressor effects can occur and may include symptoms of hypotension and bradycardia, central nervous system depression, coma, muscular weakness and/or paralysis, with difficulty breathing or respiratory failure.

[15] During the same period, the ten most frequent adverse effects to traditional cigarettes reported to US poison control centers were vomiting (80.0%), nausea (9.2%), drowsiness (7.8%), cough (7.2%), agitation (6.6%), pallor (3.0%), tachycardia (2.5%), diaphoresis (1.5%), dizziness (1.5%), and diarrhea (1.4%).

[15] Minor effects correlated with e-cigarette liquid poisoning were tachycardia, tremor, chest pain and hypertension.

[15] During the same period, the ten most frequent adverse effects to e-cigarettes and e-liquid reported to US poison control centers were vomiting (40.4%), eye irritation or pain (20.3%), nausea (16.8%), red eye or conjunctivitis (10.5%), dizziness (7.5%), tachycardia (7.1%), drowsiness (7.1%), agitation (6.3%), headache (4.8%), and cough (4.5%).

[25][26] The recent rise in the use of electronic cigarettes, many forms of which are designed to be refilled with nicotine-containing "e-liquid" supplied in small plastic bottles, has renewed interest in nicotine overdoses, especially the possibility of young children ingesting the liquids.

Organophosphates inhibit an enzyme called acetylcholinesterase, causing a buildup of acetylcholine, excessive stimulation of all types of cholinergic neurons, and a wide range of symptoms.

The initial treatment of nicotine poisoning may include the administration of activated charcoal to try to reduce gastrointestinal absorption.

[4] Acidifying the urine could theoretically enhance nicotine excretion,[31] although this is not recommended as it may cause complications of metabolic acidosis.

[4] The prognosis is typically good when medical care is provided and patients adequately treated are unlikely to have any long-term sequelae.

However, severely affected patients with prolonged seizures or respiratory failure may have ongoing impairments secondary to the hypoxia.

[14] At least at "normal" levels, as nicotine in the human body is broken down, it has an approximate biological half-life of 1–2 hours.

Cotinine is an active metabolite of nicotine that remains in the blood for 18–20 hours, making it easier to analyze due to its longer half-life.