Matthew Perry: What is ketamine infusion therapy?

Ketamine infusion therapy works by giving the drug intravenously in smaller doses than those used for anaesthesia.

“For depression, you use a lower dose than you use for chronic pain, a really lower dose than patients receive as anaesthetics,” says Dr Mario Juruena, a psychiatrist at King’s College London who specialises in treatment-resistant mental disorders.

Ketamine acts faster than traditional anti-depressants – but its effects also wear off quicker.

“It has a short half-life, so the time that the patients have the effect is quite short at some points,” Dr Juruena told the BBC, stressing the importance of monitoring patients’ mental state for relapse back into depression.

Dr Yadhu says that, unlike other mainstream anti-depressants, ketamine has been found to affect nerves that use the chemical glutamate to interact. Glutamate is the most abundant neurotransmitter in the nervous system.