Urinary and liver toxicity
Urinary toxicity occurs primarily in people who use large amounts of ketamine routinely, with 20–30% of frequent users having bladder complaints. It includes a range of disorders from cystitis to hydronephrosis to kidney failure. The typical symptoms of ketamine-induced cystitis are frequent urination, dysuria, and urinary urgency sometimes accompanied by pain during urination and blood in urine. The damage to the bladder wall has similarities to both interstitial and eosinophilic cystitis. The wall is thickened and the functional bladder capacity is as low as 10–150 mL.Management of ketamine-induced cystitis involves ketamine cessation as the first step. This is followed by NSAIDs and anticholinergics and, if the response is insufficient, by tramadol. The second line treatments are epithelium-protective agents such as oral pentosan polysulfate or intravesical (intra-bladder) instillation of hyaluronic acid. Intravesical botulinum toxin is also useful.Liver toxicity of ketamine involves higher doses and repeated administration. In a group of chronic high dose ketamine users, the frequency of liver injury was reported to be about 10%. There are case reports of increased liver enzymes involving ketamine treatment of chronic pain. Dependence and tolerance
Although the incidence of ketamine dependence is unknown, some people who regularly use ketamine develop ketamine dependence. Animal experiments also confirm the risk of misuse. Additionally, the rapid onset of effects following insufflation may increase potential use as a recreational drug. The short duration of effects promotes bingeing. Ketamine tolerance rapidly develops, even with repeated medical use, prompting the use of higher doses.
Both of these contraindications are controversial 
Poorly controlled psychosis
Severe liver disease such as cirrhosis
Pregnancy
Active substance use disorder (for serial ketamine injections)
Age less than 3 months

Side effects
At anesthetic doses, 10–20% of adults (1–2% of children) experience adverse psychiatric reactions that occur during emergence from anesthesia, ranging from dreams and dysphoria to hallucinations and emergence delirium. Psychotomimetic effects decrease adding lamotrigine and nimodipine and can be counteracted by pretreatment with a benzodiazepine or propofol. Ketamine anesthesia commonly causes tonic-clonic movements (greater than 10% of people) and rarely hypertonia. Vomiting can be expected in 5–15% of the patients; pretreatment with propofol mitigates it as well. Laryngospasm occurs only rarely with ketamine. Ketamine, generally, stimulates breathing; however, in the first 2–3 minutes of a high-dose rapid intravenous injection it may cause a transient respiratory depression.At lower sub-anesthetic doses, psychiatric side effects are prominent. Most people feel strange, spacey, woozy, or a sense of floating, or have visual distortions or numbness. Also very frequent (20–50%) are difficulty speaking, confusion, euphoria, drowsiness, and difficulty concentrating. The symptoms of psychosis such as going into a hole, disappearing, feeling as if melting, experiencing colors, and hallucinations are described by 6–10% of people. Dizziness, blurred vision, dry mouth, hypertension, nausea, increased or decreased body temperature, or feeling flushed are the common (>10%) non-psychiatric side effects. All these adverse effects are most pronounced by the end of the injection, dramatically reduced 40 minutes afterward, and completely disappear within 4 hours after the injection.