The Lotus in an elixir created by the enemies of the League of Assassins.
The Lotus elixir is capable of permanently removing the side-effects from those who bathed in the Lazarus Pit without re-opening the wounds present at the time of exposure to the Pit's waters.
The amount of the Lotus required to completely heal the intended person depends on the nature of the side-effects; Thea Queen required an entire bottle of the elixir, as she was dying from her bloodlust.
In 2016, after Thea Queen was dying of her bloodlust from being healed by the Lazarus Pit, Nyssa al Ghul was given the Lotus by Tatsu Yamashiro, a member of the Crescent Order. She offered it to Thea's brother, Oliver Queen, at one cost: killing Malcolm Merlyn so she can become Ra's al Ghul. After a big conflict, Oliver had a duel with Merlyn, in which he cut the latter's hand off and gave Nyssa the Demon's Head ring in exchange for the Lotus. Team Arrow then used the elixir on Thea, reviving her and permanently curing her bloodlust.
Sometime between 2018-2019, Thea and Nyssa used the Lotus on Roy Harper after he was healed by a Lazarus Pit. However, for unknown reasons, the potion didn't work on him. Roy theorized this was because of his past experiences with the Mirakuru.