OCD drugs work to increase serotonin levels in the brain. Standard OCD drugs used are selective serotonin reuptake inhibitors (SSRI's)
SSRI's work by preventing the reabsorption of serotonin
If after 3-4 months the SSRI isn't effective, the dosage can be increased or alternative drugs tried such as:
Tricyclics: Older form of an antidepressant drug, with more severe side effects than SSRI's. Tricyclics block the transport mechanism that reabsorbs serotonin and noradrenaline
SNRIs (serotonin-noradrenaline reuptake inhibitors). Increase levels of serotonin and noradrenaline in the synaptic cleft to reduce anxiety
