A cassette for use with an injector has a housing, and a cassette identification arrangement (cassette ID) defining a code containing information about the cassette that is detectable and decipherable by an injector. The cassette may further have a sleeve movably disposed within the housing, for holding a drug container, and a locking arrangement for interlocking the sleeve with the housing. The cassette may further have an aperture in the housing, and a cassette cap for removing a needle shield of the drug container. The cassette may have an anti-bending structure to prevent bending or flexing of the cassette cap. The injector may have a processor for controlling operational parameters of the injector and a detector communicatively coupled with the processor for detecting and communicating the cassette ID to the microprocessor to decipher the code defined therein. Also, a method of injecting a drug into a patient with an injector, wherein the sequence of actions performed by the user are controlled. Still further, a method of treating a patient in need thereof wherein a cassette containing a drug is provided and administered to the patient using an injector.