I agree. Soma is used to control the populace. If you keep them drugged up, they won't complain. In the end, the people are not interested in what the government is doing. It is kind of an update of the Roman bread and circuses idea. It keeps them entertained—out of touch—and not interested.
The government! The issue of legalizing marijuana in many states is a big these days, but not for the government of Brave New World! The government in Huxley's novel uses soma (a relaxing drug) to control the populace from feeling pain or facing hardship. Lenina takes a bunch of soma and goes "on holiday" when she first visits the reservation because it is too much for her to handle. As far as who conditions the citizens, the government and the scientists at the Hatchery genetically condition people at conception and throughout birth. Then, the caregivers are the ones who use Hypnopaedia to psychologically train children to observe the philosophies of the state.