Mood is controlled by a number of mechanisms, including hormonal balance, physiology, and various neurotransmitters. SSRIs (selective serotonin re-uptake inhibitors) and other antidepressants work by selectively increasing the levels of certain neurotransmitters in the brain. SSRI's work by preventing the synapses outside of the brain cell from absorbing serotonin. Other antidepressants such as buproprion work by preventing the re-absorption of dopamine, another neurotransmitter involved in mood stability. Finally, stimulant antidepressants such as dextroamphetamine flood the brain with building blocks of dopamine and serotonin, thus causing the brain to produce more of these neurotransmitters than it otherwise would.