Pharmacology anyone?

What specifically do you want by "affect the limbic system ... numbing or nulling?"

Do you mean dissociation, where someone may still know what is going on but not care? Or do you mean anesthetic numbing, where physical pain isn't being felt?

Ketamine may suit the description. It is a dissociative anesthetic which tends to make the person feel like what is happening is actually happening to someone else. Sometimes this is described as "it was like I was still there, but in the corner of the room."

It's a drug of abuse, and people can develop dependence. There are medical complications and risks to using it. Needless to say, nobody should be using this in real life unless under the care of a medical professional who has explictly assumed responsibility. But as for fiction, it can be a useful choice.

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Edited to add: CESAR (Center for Substance Abuse Research) has a decent article on Ketamine. Withdrawal is described in the literature, but it can be used to moderate withdrawal from opiods. Ketamine is often associated with hallucinations, either during or after use.

A pleasure.

stadol

stadol is very addictive and there are more than one way to deliver it to a victim. it is very effective. here is a blurb from the FDA it directly effects the limbic system (especially in the limbic system (frontal cortex, temporal cortex, amygdala, and hippocampus), thalamus, striatum, hypothalamus, and midbrain as well as laminae I, II, IV, and V of the dorsal horn in the spinal cord. Kappa receptors are localized primarily in the spinal cord and in the cerebral cortex.)) I have used stadol before and it is quick acting, takes affect in a almost immediately and is widely abused. I went through withdrawal also when I changed to a different med and the withdrawal is extreme to say the least. I would go with Stadol when you use enough of it you don't care about anything or anyone (true story) you are truly disassociated from the rest of the world and your self.