An at least partly implantable system for injecting a substance into a patients body, in particular a penis erection stimulation system, comprises one or more infusion needles disposed within and implanted along with one or more housings adjacent the patients left and right corpora cavernosa. A reservoir and a pump are also implanted inside the patients body to supply the infusion needle with infusion liquid. A drive unit also adapted for implantation inside the patients body is arranged for advancing and retracting the tip end of the infusion needle such that it penetrates the housing at least in two different penetration areas either simultaneously or in immediate time succession, thereby injecting drugs along with the infusion liquid into the patients body for stimulating penis erection. The drive unit is configured to laterally displace the tip end of at least one infusion needle in at least two different lateral directions to different penetration sites within said at least one penetration area.
