A system for controlling a drug delivery profile, the system comprising: at least one drug pump (105, 152) that produces a drug flow, wherein the at least one drug pump dispenses at least a first drug; at least one carrier fluid pump (105, 152) that produces a carrier fluid flow; a flow junction structure configured to receive the drug flow and the carrier fluid flow to produce a mixed flow; a fluid path for carrying the mixed flow between the flow junction structure and a delivery point; a control module configured to control the drug delivery profile at the delivery point by controlling a drug flow rate and a carrier fluid flow rate such that a ratio between the drug flow rate and the carrier fluid flow rate is substantially fixed over a range of time, and the mixed flow is varied to achieve a particular drug delivery profile, wherein the control module adjusts the drug delivery rate to achieve a predicted drug delivery rate calculated using at least a model of the mixed flow, wherein the mixed flow is modeled using a Taylor dispersion equation that can be represented as: ∂ c ̅ ∂ t + u ̅ ∂ c ̅ ∂ x = R 2 u ̅ 2 48 D + D ∂ 2 c ̅ ∂ x 2 where D represents a molecular diffusion coefficient, u represents a mean or average axial velocity of fluid through a tube, x represents an axial distance along the tube, t represents time, R represents a radius of the tube, and c represents an average of concentration of a substance calculated over a cross-section of the tube; and at least one controllable valve disposed upstream from the flow junction structure, wherein the at least one controllable valve is configured to exert a controllable resistance to flow and wherein the control module controls the drug delivery profile at the delivery point by controlling a flow through the controllable valve. at least one drug pump (105, 152) that produces a drug flow, wherein the at least one drug pump dispenses at least a first drug; at least one carrier fluid pump (105, 152) that produces a carrier fluid flow; a flow junction structure configured to receive the drug flow and the carrier fluid flow to produce a mixed flow; a fluid path for carrying the mixed flow between the flow junction structure and a delivery point; a control module configured to control the drug delivery profile at the delivery point by controlling a drug flow rate and a carrier fluid flow rate such that a ratio between the drug flow rate and the carrier fluid flow rate is substantially fixed over a range of time, and the mixed flow is varied to achieve a particular drug delivery profile, wherein the control module adjusts the drug delivery rate to achieve a predicted drug delivery rate calculated using at least a model of the mixed flow, wherein the mixed flow is modeled using a Taylor dispersion equation that can be represented as: ∂ c ̅ ∂ t + u ̅ ∂ c ̅ ∂ x = R 2 u ̅ 2 48 D + D ∂ 2 c ̅ ∂ x 2 where D represents a molecular diffusion coefficient, u represents a mean or average axial velocity of fluid through a tube, x represents an axial distance along the tube, t represents time, R represents a radius of the tube, and c represents an average of concentration of a substance calculated over a cross-section of the tube; and D represents a molecular diffusion coefficient, u represents a mean or average axial velocity of fluid through a tube, x represents an axial distance along the tube, t represents time, R represents a radius of the tube, and c represents an average of concentration of a substance calculated over a cross-section of the tube; and at least one controllable valve disposed upstream from the flow junction structure, wherein the at least one controllable valve is configured to exert a controllable resistance to flow and wherein the control module controls the drug delivery profile at the delivery point by controlling a flow through the controllable valve.