Implantable devices and methods for controlled drug delivery are provided. The device includes a device structure deformable between a retention shape and a low profile shape for deployment in the bladder of a patient and has a drug reservoir lumen in which a drug formulation is housed. The device also includes a buoyancy retention portion, which includes a volume of entrapped air or a gas-generating or effervescent powder which will generate a volume of entrapped air following contact with urine in the bladder. The buoyancy retention portion may include a water permeable and/or biodegradable wall, which can release the entrapped air following drug release, to cause the device to sink into the bladder neck to facilitate device expulsion without the need for a device retrieval medical procedure.