A system for optimizing a patient's basal insulin dosage regimen over time, comprising a display unit and a drug delivery assembly, the drug delivery assembly comprising: - a drug delivery device (20, 320) comprising: - a drug reservoir or means for receiving a drug reservoir, - an outlet for the drug, and - an actuatable drug expelling mechanism for expelling drug from the reservoir and out through the outlet, and - a cap (10, 310) releasably mountable on the drug delivery device and adapted to cover the outlet in a mounted position, the cap forming a patient unit, the patient unit comprising: - a blood glucose meter for determining a blood glucose value from a blood sample, - first controller and memory means adapted to: (i) store data representing an initial basal insulin dosage regimen, the dosage regimen comprising a recommended amount of an insulin-containing drug to be taken at recommended intervals, (ii) determine from blood glucose values determined at a plurality of times whether and by how much to vary the patient's present recommended amount of the insulin-containing drug in order to maintain the patient's future blood glucose level measurements within a predefined range, and (iii) create a blood glucose value log representing blood glucose values as a function of time, and - means for transmitting log data to the display unit, the display unit comprising: - display means, and - means for receiving log data from the drug delivery assembly, characterized in that the display unit comprises: - means for receiving log data from the drug delivery assembly, - second controller and memory means adapted to: (i) store the received log data, and (ii) control the display means to at the same time display the blood glucose value log data and a recommended amount of the insulin-containing drug log as a function of time. wherein: (i) the second controller means is adapted to calculate the recommended amount of the insulin-containing drug log based on the received blood glucose value log, or (ii) the first controller and memory means are adapted to create a recommended amount of the insulin-containing drug log representing recommended amounts as a function of time, the recommended amount of the insulin-containing drug log used by the second controller means being received from the patient unit. - a drug delivery device (20, 320) comprising: - a drug reservoir or means for receiving a drug reservoir, - an outlet for the drug, and - an actuatable drug expelling mechanism for expelling drug from the reservoir and out through the outlet, and - a drug reservoir or means for receiving a drug reservoir, - an outlet for the drug, and - an actuatable drug expelling mechanism for expelling drug from the reservoir and out through the outlet, - a cap (10, 310) releasably mountable on the drug delivery device and adapted to cover the outlet in a mounted position, the cap forming a patient unit, - a blood glucose meter for determining a blood glucose value from a blood sample, - first controller and memory means adapted to: (i) store data representing an initial basal insulin dosage regimen, the dosage regimen comprising a recommended amount of an insulin-containing drug to be taken at recommended intervals, (ii) determine from blood glucose values determined at a plurality of times whether and by how much to vary the patient's present recommended amount of the insulin-containing drug in order to maintain the patient's future blood glucose level measurements within a predefined range, and (iii) create a blood glucose value log representing blood glucose values as a function of time, and (i) store data representing an initial basal insulin dosage regimen, the dosage regimen comprising a recommended amount of an insulin-containing drug to be taken at recommended intervals, (ii) determine from blood glucose values determined at a plurality of times whether and by how much to vary the patient's present recommended amount of the insulin-containing drug in order to maintain the patient's future blood glucose level measurements within a predefined range, and (iii) create a blood glucose value log representing blood glucose values as a function of time, - means for transmitting log data to the display unit, - display means, and - means for receiving log data from the drug delivery assembly, - means for receiving log data from the drug delivery assembly, - second controller and memory means adapted to: (i) store the received log data, and (ii) control the display means to at the same time display the blood glucose value log data and a recommended amount of the insulin-containing drug log as a function of time. (i) store the received log data, and (ii) control the display means to at the same time display the blood glucose value log data and a recommended amount of the insulin-containing drug log as a function of time. (i) the second controller means is adapted to calculate the recommended amount of the insulin-containing drug log based on the received blood glucose value log, or (ii) the first controller and memory means are adapted to create a recommended amount of the insulin-containing drug log representing recommended amounts as a function of time, the recommended amount of the insulin-containing drug log used by the second controller means being received from the patient unit.