How does poison work in FATE? Secret, previously administered poison (say, in a drinking class) is an aspect that, like most investigation aspects, doesn't expire 'next turn' but will sit and wait. Extremely fast poison can just be thought of as damage on the weapon, it does damage when it hits. (Say, acid weapons or most of the fae nasties that Harry runs into.) What if someone gets hit with a poisoned weapon that would last for at least a few rounds, preferably how to do it over a few minutes/hours?
The answer is going to depend on what role the poison is serving.
Wraith808's answer using the Venomous feature and tazers will work if it's a feature of the opponents and not expected to last a long time.
If it's part of a conflict with a poisoner, you can give the loser the aspect "Unknowingly poisoned with x venom" as a concession or loss. As an aside, FATE doesn't do well with secret information. Players are expected to know what's happening, even if their characters don't.
If it's a big plot point, you could model the poison as a character with aspects, a plot stress track and skills similar to It's On Fire. How they get poisoned in the first place should be the result of losing a conflict somehow, or a consequence taken during a conflict.
An example poison could be:
Given the complexity of this solution, you will want to use this in situations where the poison is supposed to hang around a long time and it can cause other complications.
In addition, on
So, taking the two together, I'd make a regular weapon attack, and apply the Poisoned aspect if a consequence is taken. Then use the guidelines from Venomous to take over from that point, using the rating for the poison.