Deadpool's primary power is accelerated healing factor, shown by different writers at different levels of efficiency. Artificially endowed by the Weapon X program, this enables him to regenerate any destroyed tissue at a super-human rate as well as making him immune to known diseases. An unanticipated side effect was an acceleration of the cancerous tumors he was suffering at the time, causing them to quickly spread across his body. Because oft his, his healing factor supercharged his cancer resulting in massive scar tissue causing his appearance to be severely deformed.
Deadpool's brain cells similarly affected, with dying brain cells being rejuvenated at a super accelerated rate. This allows him to recover from any head injuries, and it renders him nearly invulnerable to psychic and telepathic powers, as the altered or damaged brain cells quickly regenerate to their original state. It is also the cause of his psychosis and mental instability. It is sometimes implied that his factor merely bolstered and made his mental issue worse, as a young Wade Wilson was shown as a withdrawn, disturbed young kid caught in his zany daydreams and, upon losing his healing factor, Deadpool did not regain his sanity.
Deadpool's healing factor is strong enough he has survived complete incineration and decapitation more than once. Although hid head normally has to be reunited with his body to heal the wound, he was able to regrow his after having it pulverized by the Hulk. Unlike Wolverine's natural healing factor, Deadpool's is mentally driven. Similar to Wolverine, his healing factor also affects his physical attributes by increasing them to super-human levels.
Though in earlier years he also had super-human strength that detail has apparently been forgotten. Deadpool's body is highly resistant to most drugs and toxins. For example it is very difficult for him to become intoxicated. He can be affected by certain drugs such as tranquilizers, if he is exposed to a large enough dosage. Deadpool's healing factor also slows the aging process. He is still alive 800 years in the future when the new X-Force encounter him
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