List of causes of regeneration

The causes of regeneration, especially amongst Time Lords, were many and varied. They ran the gamut from simple desire to change, to life-threatening maladies which typically resulted in human death. The following are the known causes of regeneration of specific Time Lords.

The Doctor

 * First regeneration/second incarnation: Died of old age, which wore his elderly body thin until he finally collapsed from exhaustion. (TV: The Tenth Planet)
 * During second incarnation: Shot in the head when confronted by guards on Skybase, causing damage to his skull and frontal lobe; subsequent fall broke his nose, jaw, right femur, and collarbone, along with some spine damage; an injection of Shiner DNA delayed the regeneration and kept him alive long enough for his body to go into a six-month healing coma to recover on its own (PROSE: The Indestructible Man).
 * Second regeneration/third incarnation: Forced to change his appearance as part of his exile at the hands of the Time Lords. (TV: The War Games, COMIC: The Night Walkers)
 * During third incarnation: Fell off a building during a struggle, and began to regenerate into the Fourth Doctor as the Nurazh attempted to take over the Doctor's mind; unable to cope with two Time Lord minds at the same time, the Nurazh perished, thus healing the Doctor back to his Third incarnation. (PROSE: The Touch of the Nurazh)
 * Third regeneration/fourth incarnation: Caused by exposure to The Great One's highly unstable web of Metebelis crystals. (TV: Planet of the Spiders)
 * Alternate third regeneration/fourth incarnation: Shot by Magdalena on the planet Dust after defeating the Remote. (PROSE: Interference - Book Two) This timeline was created when the Eighth Doctor accidentally diverted his third self's TARDIS, and was later undone. (PROSE: The Ancestor Cell)
 * Fourth regeneration/fifth incarnation: Caused when rotated the Pharos Project radio telescope so as to force the Fourth Doctor to fall to the ground while he was manually programming it. (TV: Logopolis)
 * Fifth regeneration/sixth incarnation: Caused by Spectrox toxaemia, contracted after contact with unrefined spectrox. (TV: The Caves of Androzani)
 * Sixth regeneration/seventh incarnation: Caused by injury from the Rani's attack on the TARDIS. (TV: Time and the Rani) Accounts indicated the Doctor hit his head (PROSE: Head Games); however, he was also suffering from a chronal energy drain after his confrontation with the Lamprey (PROSE: Spiral Scratch).
 * Seventh regeneration/eighth incarnation: Uniquely for the Doctor, this regeneration happened after his physical death. A gang shootout in San Francisco caused him near-fatal injuries, exacerbated by surgery at Walker General Hospital surgery which attempted to explore his unearthly physiology. The surgery only succeeded in damaging his cardiovascular system far beyond repair, with the anaesthetic damaging his physiology further by delaying the regeneration. He regenerated and came back to life in the morgue. (TV: Doctor Who)
 * Alternate seventh regeneration: In an alternative timeline in which the Nazis used technology taken from Ace in Colditz to win World War II, the Doctor arranged to be shot and killed in 1955. (AUDIO: Colditz) He subsequently infiltrated the Reich as "Johann Schmidt" to erase this new timeline. (AUDIO: Klein's Story).
 * During eighth incarnation: Stabbed in one of his hearts and began to regenerate, but healed by the energies of Anti-Time then controlling his body (AUDIO: Zagreus); chest was crushed by a sandbag, causing him to start regenerating again, but saved due to one heart having been transplanted into Sabbath, giving him a link to life that allowed his body to heal. (PROSE: ''Camera Obscura)
 * Eighth regeneration/the "War Doctor": Caused by crashing in a spaceship onto the planet Karn. His regeneration was assisted by the Sisterhood of Karn after they gave him potions and they persuaded him to be part of the Last Great Time War. (TV: The Night of the Doctor)
 * Ninth regeneration/Ninth incarnation: Caused by his body growing weaker after helping to bring back Gallifrey from the Time War and place it in a different dimension. He remarked that his body had "grown a bit thin". (TV: The Day of the Doctor)
 * Tenth regeneration/tenth incarnation: Caused by cellular degeneration from absorbing the energies of the time vortex from Rose Tyler in order save her life and restore the TARDIS. (TV: The Parting of the Ways)
 * During tenth incarnation: Partial regeneration after being exterminated by a Dalek; (TV: The Stolen Earth) aborted by channelling the energy into his severed hand that would have changed his appearance after allowing it to heal the damage sustained by the attack. This led to the two-way biological metacrisis that spawned the Meta-Crisis Tenth Doctor and the Doctor Donna (TV: Journey's End)
 * Eleventh regeneration/eleventh incarnation: Caused by radiation poisoning when the Doctor sacrificed himself to spare Wilfred Mott. He absorbed all the radiation from the nuclear bolt used to power the Immortality Gate. Trivial cuts healed instantly. The regeneration, though, took a long time rather than instantly. (TV: The End of Time)

Romana

 * First to second incarnation: Decided it was time for a change, regenerating into several different forms before settling on the features of Princess Astra. (TV: Destiny of the Daleks)
 * Second to third incarnation: Regenerated in preparation for the Second War in Heaven, developing a body and attitude more suited for combat. (PROSE: The Shadows of Avalon)
 * The second incarnation stareds to regenerate due to contact to the decaying Eye of Harmony inside the Matrix. (AUDIO: Renaissance. This regeneration didn't take hold due to K9 Mark II removing her from the Matrix. (AUDIO: Ascension)
 * Third to fourth incarnation: Managed to survive the Second War in Heaven, although this may have entailed a regeneration. (PROSE: Tomb of Valdemar)

The Master

 * When his TARDIS was pulled into a black hole by the Second Doctor, Koschei used up most his regenerations escaping it. (PROSE: The Dark Path)
 * Shot by Ace after receiving a new set of regenerating nanites from the Tzun. However, these were apparently only effective in the short term. (PROSE: First Frontier)
 * During the Last Great Time War, the Time Lords resurrected the Master, apparently giving him a new regeneration cycle in the process (TV: The Sound of Drums) as, when was shot by Chantho, he regenerated into a . (TV: Utopia)

Rassilon

 * Rassilon was said to have achieved a cycle of perpetual regeneration, becoming immortal. (TV: The Five Doctors)

K'anpo Rimpoche

 * K'anpo Rimpoche was attacked by the Eight Legs on Earth. He regenerated into the form of Cho Je, a projection of his own mind. (TV: Planet of the Spiders)

Borusa

 * Borusa regenerated at least three times, and had at least four incarnations. (TV: The Deadly Assassin, TV: The Invasion of Time, TV: Arc of Infinity, TV: The Five Doctors)

Chronotis

 * Salyavin used up his thirteenth and final incarnation when he was attached by the Sphere. However, when his Type 12 TARDIS was sent backwards, it altered his personal timeline and brought him back to life. (HOMEVID: Shada/WC: Shada)

Rallon

 * Rallon nitiated all twelve of his regenerations to force the Celestial Toymaker out of his body. (PROSE: Divided Loyalties)

Azmael

 * In his thirteenth and final body, Azmael regenerated past his limit, killing him and Mestor, who possessed Azmael's body after his own was destroyed. (TV: The Twin Dilemma)

Iris Wildthyme

 * Iris Wildthyme regenerated following a lengthy period of illness following the consumption of a live Kaled mutant. (PROSE: The Scarlet Empress)

The War Chief
Because of this, he can no longer regenerate.
 * The War Chief underwent a faulty regeneration after being shot by War Lords; lack of medical care and the scale of the damage sustained resulted in his new form appearing like two bodies fused together. (PROSE: Timewyrm: Exodus)

The Monk

 * The Monk regenerated at least once. (PROSE: No Future, AUDIO: The Book of Kells)

Ruath

 * Ruath drained every drop of her blood from her body to restore Vampire Lord Yarven. Yarven subsequently turned her into a vampire. (PROSE: Goth Opera)

Innocet

 * Innocet was killed by a Quences-possessed Badger to protect the Doctor (PROSE: Lungbarrow).

I.M. Foreman

 * As a priest, I.M. Foreman had been given the gift of regenerations. This made twelve different individuals, who were created by his body absorbing the DNA around him; all regenerations were caused by the Third Doctor sending the first twelve back to Gallifrey's past so that they fell from a great height and regenerated into the next one. (PROSE: Interference - Book One, Interference - Book Two)

The Corsair

 * The Corsair regenerated several times, with "a couple" of his incarnations being female. He was back to male by the time he was killed by House. (TV: The Doctor's Wife)

River Song

 * First to second incarnation: As a little girl, Melody Pond, later known as River Song, regenerated on the streets of New York City in 1970 due to being shot by Amy Pond. (TV: The Impossible Astronaut, Day of the Moon)
 * Second to third incarnation: Melody later regenerated in Hitler's private study in 1938 after the Führer accidentally shot her while fearing the Teselecta. She later used up all of her remaining regenerations to heal the Doctor from a poison that she had infected him with. (TV: Let's Kill Hitler)