Demon Blood

Azazel: Demon blood is better than Ovaltine, vitamins, minerals. It makes you big and strong. – , 4.03 In The Beginning

Consuming the blood of a demon - technically the demon infected blood of the person said demon is possessing - gives or enhances superhuman abilities. Consumption on a regular basis can lead to addiction.

2.22 All Hell Breaks Loose: Part Two

File:Baby Sam in 2-21.jpg

Sam as a baby.

Azazel reveals that he fed Sam his blood on the night of his six month birthday, also revealing that he did so to all the other Special Children. Demon blood either gives or enhances psychic powers.

These powers vary from premonitions to superstrength, telekinesis and the touch of death. These power may begin as minor, but if the indidivual starts to practise, thay can become major powers (eg. Ava & Max Miller.) For more on this see: Special Children.

After Azazel died, Sam's psychic powers seemingly disappeared.

4.03 In The Beginning

When Dean encounters Azazel in 1973, he reveals what he plans to do to Sam:

Cause you know what I'm gonna do to your sibling? I'm gonna stand over their crib and I'm gonna bleed into their mouth. Demon blood is better than Ovaltine, vitamins, minerals, it makes you big and strong.

4.04 Metamorphosis

While exorcising a demon, it says to Sam that it knows "all the things you and this demon bitch do in the dark."

When Dean tells Sam what Azazel revealed to him, he is shocked to learn that Sam knew of this for over a year. Later Sam says:

I've got demon blood in me, Dean! This disease pumping through my veins, and I can't ever rip it out or scrub it clean! I'm a whole new level of freak! And I'm just trying to take this - this curse... and make something good out of it. Because I have to.

At the end of the episode Sam says he has made a choice, not for Dean or God but for himself, to stop using his powers.

4.07 It's The Great Pumpkin, Sam Winchester

Given that Sam has the ability to kill Samhain Sam must be drinking blood at this time. He must stop soon after.

4.09 I Know What You Did Last Summer

Through a flashback, Sam reveals that while Dean was in Hell, Ruby taught Sam how to tap into his buried powers, preparing him to take on Lilith. He doesn't mention that part of this included feeding on Ruby's blood.

4.10 Heaven And Hell

Ruby alludes to the blood consumption when she tells Sam his abilities are getting flabby "You know how. You know what you got to do." But Sam says "No, I'm not doing that anymore."

4.12 Criss Angel Is A Douchebag

Ruby visits Sam and Sam again refuses to return to drinking blood (although he doesn't explicitly call it this) However at the end of the episode, he changes his mind and goes to meet with Ruby, confirming he is ready to do it.

4.16 On The Head Of A Pin

Sam drinking Ruby's blood.

Sam is worried about that Dean is emotionally unable to torture information out of Alistair. After locating him with Ruby's spell, he began to doubt his own strength, as Alistair had resisted his previous attempts at exorcism, so he drinks some of Ruby's blood, giving him not only the power to exorcise Alistair but kill him.

4.18 The Monster At The End Of This Book

Sam is worried that Chuck Shirley knows about him consuming Ruby's blood and that he will tell Dean, so he confronts him alone. Chuck says he does know about Sam drinking demon blood, but that he didn't write it down because he was afraid it would make Sam "look unsympathetic". He challenges Sam about his motivation for doing it, asking whether he does it because it makes him feel in control.

4.20 The Rapture

Desperate for a fix, Sam drinks demon's blood in front of Dean & Castiel.

Sam becomes increasingly agitated as the demon blood, presumably from Ruby, he is carrying in a flask runs out, and Ruby won't return his phone calls. When he tries to exorcise a demon with his powers, he fails. When Dean asks what's going on, and says he is scared about what is happening to Sam, Sam says he doesn't know but that he is scared too. Later during the fight with the demons, Sam takes the opportunity to cut one of the demon's and drink her blood. He uses his powers to exorcise the demon possessing Amelia Novak.
Back on the road, Sam waits for a response from Dean about the revelation of his blood drinking. Dean seems weary and won't talk about it. Sam gets a call from Bobby saying he needs to see them - unbeknownst to him arranged by Dean. They get to Bobby's place, and he pretends to show them something in his panic room, but it is a ruse to trap Sam in there.

4.21 When The Levee Breaks

Withdrawing from the Demon Blood, Sam hallucinates, fits and is flung bodily around Bobby's Panic Room. With no lore to guide them Dean and Bobby are unsure if Sam can survive.

Castiel tells Dean that Sam could kill Lilith but consuming that much Demon Blood would make him inhuman.

When Sam is released by Castiel he meets up with Ruby and feeds on her blood again. She says his appetite has increased, and that this is a sign he his getting stronger.

4.22 Lucifer Rising

Sam is distressed when the demon possessing a woman allows her personality to show through, so Sam is confronted with the fact that drinking her blood will kill her. Despite this, as he approaches his showdown with Lilith, he does just that.

After killing Lilith, Ruby reveals to an appalled Sam that she has been working with Lilith all along to free Lucifer. She tells Sam he didn't need the demon blood, that the choices he has made all year have helped him tap into his own power.

As Lilith's blood forms a spiral on the chapel floor, it frees Lucifer from his imprisonment.

5.01 Sympathy For The Devil

Dean asks Sam if he is "jonesing for another hit of bitch blood". Sam replies "It's weird. Uh, tell you the truth, I'm fine. No shakes, no fever. It's like whoever...put me on that plane cleaned me right up."

5.02 Good God Y'All

When Sam kills two townspeople he thinks with Ruby's knife, he appears drawn to the blood. He tells dean he wishes he could save people like he used to. Dean retorts - "you mean when you were all hopped up on demon blood?" This leads to Sam's decision to leave dean, and hunting, becasue he can't trust himself.

5.03 Free To Be You And Me

When demons kills some hunters, their friends demons confront Sam. He confesses that he was the one who had started the Apocalypse as they had heard from the demons, but the hunters want him to drink a vial of demon blood and wipe out all the demons in the town. Sam refuses and he's attacked by Hank, who force-feeds him the blood. Sam spits it back in his face, then beats them up badly, and they leave.

5.14 My Bloody Valentine

When Famine arrives and awakes in people an irresistible urge for the thing they hunger most, Sam again starts to crave Demon Blood. He gets Dean to handcuff him to the bathroom sink, but Famine sends two demons to purposefully tempt him. Sam drinks their blood, and then uses his powers to go and exorcise the other demons Famine brought with him, resisting the urge to drink more blood. When Famine ingests all the demons, Sam turns his powers on him, seemingly destroying him.

Dean and Castiel then lock Sam in Bobby's Panic Room to detox.

5.21 Two Minutes To Midnight

While discussing Sam's plan to say yes to Lucifer and jump in the hole, Castiel reminds him about the demon blood. To take in Lucifer, Castiel says, would be more than Sam has ever drunk. He says it "strengthens the vessels, keeps it from exploding," and notes that Nick, Lucifer's current vessel, is drinking "hundreds of gallons" of the stuff.
Speculation: This may have been Ruby's intent all along in getting Sam addicted to demon blood - strengthening him to become Lucifer's vessel.