Embodiments of an implantable electrolytic pump include an electrolysis chamber, a drug chamber and an osmosis chamber, the osmosis chamber having a first portion in contact with the drug chamber and a second portion exposed to facilitate contact with a surrounding fluid. The pump further includes a cannula for conducting liquid from the drug chamber and electrolysis electrodes within the electrolysis chamber for causing generation of a gas therein, the electrolysis and drug chambers being in contact such that gas electrolysis within electrolysis chamber forces fluid from the drug chamber into the cannula, contact between the drug chamber and the osmosis chamber permitting fluid admitted into the osmotic chamber from the surrounding fluid to offset volume loss from the drug chamber and prevent buildup of vacuum pressure thereon.