CO2 (carbon dioxide) is a gas that plants use for photosynthesis, the process of converting light into energy and sugars. By increasing the CO2 levels in your grow room or tent, you can increase the photosynthesis rate of your plants and thus their growth and yield. However, there is no conclusive evidence that CO2 can increase THC levels in cannabis buds. Some studies have shown that CO2 can increase THC levels in some strains, while others have shown no effect or even a decrease. Therefore, CO2 supplementation may not be worth the cost and effort for most home growers.