In a saucepan, bring 2 cups of water to a boil.
Once boiling, remove the saucepan from heat and add the tea bags. Let steep for about 5 minutes.
In the meantime, mash 1 cup of fresh blackberries in a bowl using a fork or potato masher until they release their juices.
Remove the tea bags from the saucepan and add the mashed blackberries and honey (or sugar) to the hot tea. Stir until the sweetener is dissolved.
Add the fresh sage leaves to the mixture and let it steep for an additional 5 minutes.
Strain the tea through a sieve to remove the blackberry pulp and sage leaves, pouring it into a pitcher.
Allow the tea to cool to room temperature, then refrigerate until cold.
To serve, fill glasses with ice and pour the chilled tea over the ice. Garnish with fresh blackberries and lemon slices, if desired.