Help with quest script?

[JoRakhar]

So I need to set up a quest script to have an effect script run at random intervals.

 

The effect script triggers a visual effect during chem withdrawal.

 

I'm trying to set the effect to happen randomly until the addiction is cured.

 

I just started messin' with scripts though and currently drawing a total blank.

 

This is the effect script:

ScriptName MorphineWithdrawalEffect

begin ScriptEffectStart
imod MorphineWithdrawal 
end