Apparatus (30) for drug administration is provided, including an ingestible capsule (32), which includes a drug (36), stored by the capsule (32), and an environmentally-sensitive mechanism (18), adapted to change a state thereof responsively to a disposition of the capsule (32) within a gastrointestinal (GI) tract (50) of a subject. The capsule (32) further includes first and second electrodes (16), and a control component (14), adapted to facilitate passage of the drug (36), in response to a change of state of the environmentally-sensitive mechanism (18), through an epithelial layer of the GI tract (50) by driving the first and second electrodes (16) to apply a series of pulses at a current of less than about 10 mA, at a frequency of between about 12 Hz and about 24 Hz, and with a pulse duration of between about 0.5 milliseconds and about 3 milliseconds. Other embodiments are also described.