A penis erection stimulation system comprises a fully implantable drug delivery device for delivering a drug in relation to a penis to achieve erection of the penis. The drug delivery device may comprise a catheter adapted to be implanted in the corpora cavernosa of a penis or in close proximity thereto in order to deliver drugs through said catheter. Alternatively, one or more infusion needles may be disposed within and implanted along with one or more housings adjacent the patient's left and right corpora cavernosa. A reservoir and a pump may also be implanted inside the patient's body to supply the infusion needle with infusion liquid. A drive unit also adapted for implantation inside the patient's 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 patient's body for stimulating penis erection.