Berserker - Psycho makes you do more damage, so I assume that it works by suppressing your inhibitions and dialing up your aggression. By this logic, applying these effects to an enemy would likely make them just want to fight, regardless of who or what.
Knockout - Med-X is the Fallout universe's version of Morphine, which is named for Morpheus, the Greek god of dreams. In addition to acting as a painkiller, morphine is known for its drowsiness-inducing effects, so it stands to reason that a large dose of it would knock you out pretty quickly.
Paralysis - Steady reduces your weapon spread, so I assume it's some kind of muscle relaxant. A large enough dose of it administered directly to the bloodstream would likely result in you losing control of your muscles.
Poison - This one is pretty self-explanatory, really.
Panic - Jet increases your action points so I assume it works similarly to some kind of synthetic adrenaline. Fear and adrenaline are closely linked, and the physiological signs of one are more or less the same as the other (faster heartbeat, shortness of breath, dilated pupils, etc.) A Stimpak is a stimulant, as the name implies, which would help to enhance the effect of the Jet.
Blindness - Cateye improves your night vision, so I assume it works by dilating your pupils to allow more light to enter. In low light, this is beneficial but if you've ever been to the optometrist and had those drops put in your eyes (you know the ones I mean) and then set foot outside into the sunlight, you'll know that you are effectively blind and can't do much of anything other than covering your eyes. As far as the Whiskey goes, being drunk won't help your fine motor skills any.
Overthink - Mentats increase your intelligence, and I assume it works by causing the neurons in your brain to fire either more rapidly or causing more of them to fire at once. Turbo slows down time, and I assume it works by stimulating your nerves, enhancing your reflexes so that everything appears to be happening slowly. Combining the two effects means that your entire nervous system is all lit up at once, which would likely be mentally and physically exhausting, hence the unconsciousness. However, this would also likely be extremely traumatic for a small subsection of people, whose bodies can't handle the overstimulation, hence the head asplode.
Bloat - Buffout increases strength, so I figure it works by rapidly developing muscle mass. Hydra heals crippled limbs, so I figure it stimulates bone growth. Combine these two effects with a dash of Cazador poison as an inflammation agent and you should get rapid and unchecked growth that mangles the body as the victim struggles. There would also likely be a small chance that the growth would continue until the skin can no longer contain the rapidly-expanding bodymass, resulting in gibbing. Originally, I had this scripted to physically increase the scale of the victim over time, but unfortunately, the KillActor function doesn't fire reliably on any actor whose scale has been altered, so I had to nix that.
Pacify - Ant Queen Pheromones can cause one person to fall in love with another (or at least make them more suggestible). Alcohol, such as Vodka, can also cause "I love you, man!" tendencies. Diluting the pheromones with vodka could conceivably cause a temporary stupor effect where the target feels calm and doesn't want to fight anyone.
Incubator - The Centaur blood would act as a source of food/nourishment as well as a radiation source, while the Buffout would act as a growth accelerator. Combine them together with DNA from the creature egg and a baby creature could conceivably gestate in seconds!
Irradiate - Dirty Water, if injected into the bloodstream, would likely expose the target to dangerous levels of radiation.