It is vital for your anaesthetist to know what drugs you have used in the past and when. Street or ‘recreational’ drugs, such as heroin, LSD and cocaine, can strongly influence the anaesthetic. Cocaine and ecstasy are two drugs that excite the nervous system. They may excite your heart, producing dangerous swings in blood pressure and heart rate, both during and after the operation. Drugs such as LSD can produce hallucinations, which may cause flashbacks in the postoperative period. As a general rule, it is safer not to use any of these drugs for at least one week before your anaesthetic and operation.