Bupropion ER 300mg is an extended-release tablet used to treat major depressive disorder and assist with smoking cessation. It functions by increasing norepinephrine and dopamine levels in the brain through reuptake inhibition, improving mood and reducing nicotine cravings. The ER form provides a steady release of medication, enabling once-daily dosing for better adherence and consistent blood levels. The 300mg dose is often used in patients requiring higher therapeutic effect, while balancing efficacy and tolerability.