Afflictions and illnesses

The following are various afflictions and illnesses featured in My Little Pony Friendship is Magic and accompanying merchandise.

Cold
In Winter Wrap Up, Spike gets a cold after falling into cold water; his only noticeable symptom is sneezing. During the song in Hearts and Hooves Day, Sweetie Belle remarks that one of Cheerilee's potential suitors has "a terrible cold"; the pony has a reddened nose, blood-shot eyes, a thermometer in his mouth, and a hot-water bottle on his head.

Collective amnesia
Applejack describes the Crystal Ponies' memory loss in season three's opener as "some kind of collective amnesia." Twilight Sparkle and her friends seek out more information about the Crystal Empire so they can use the Crystal Ponies' magic to protect the empire, but find that they don't remember anything. The Crystal Pony that Twilight interviews can't remember anything before King Sombra came to power, and says that although they've been gone a thousand years, King Sombra's rule "feels like it was just yesterday." Once the interviews prove fruitless, the ponies head to the library, where they meet a librarian pony who can't remember where the history section is or whther she even works at the library. The ponies find the information they seek and decide to hold a Crystal Fair to "renew the spirit of love and unity in the empire so they could protect it from harm", according to the book Twilight reads.

The Crystal Fair does jog the Crystal Ponies' memories, they recall the Crystal Heart–and the librarian recalls that she really does work at the library. By the end of the episode, the Crystal Ponies even manage to recognize that the replacement Crystal Heart that Twilight fashioned isn't the real Crystal Heart, but the real Crystal Heart is eventually restored and the Crystal Ponies' magic protects the Crystal Empire once again.

Cutie pox
"Cutie pox" are featured in the eponymous episode The Cutie Pox, which Twilight describes from a book: "This puzzling pony plague afflicted a population of ponies back in the Paleopony period. Random cutie marks appeared all over the ponies' bodies, causing them to be forced to perform, without stopping, all the talents that came with them. The cause of the breakout was never discovered, and the cutie marks disappeared as mysteriously as they arrived." Apple Bloom contracts cutie pox in the episode after an overdose of Heart's Desire plant petals. The pox is cured by the flower that grows from the Seeds of Truth supplied by Zecora, which sprout only in the presence of a truthful confession.

Feather flu
A number of ponies contract feather flu in Hurricane Fluttershy. Initially Rainbow Dash accuses Thunderlane of trying to get of out of setting a new tornado speed record with all the other Pegasus ponies when she hears coughing. Afterward, the pony who was standing behind Thunderlane, Blossomforth, coughs too. Rainbow Dash lists off at least seven other Pegasi who contracted the flu, with Thunderlane said to be at the hospital. At one point Twilight Sparkle sprays Thunderlane to create a "germ-free environment."

Food poisoning
Some ponies suffer from food poisoning in Applebuck Season when Pinkie Pie accidentally serves "baked bads" after Applejack's sleep-deprived attempts to help with muffin baking go awry. "Nurse Redheart" and "Nurse Tenderheart" tend to a number of ponies who are seen squirming and writhing on their beds, many of them green-faced; some of them vomit.

Greed-induced growth
Zecora explains in Secret of My Excess that Spike's greed is making him grow into a monster. At the end of the episode he returns to normal after Rarity reminds him of his act of generosity towards her when he gave her a gem he's been saving for himself for his birthday.

Hay fever
In The Cutie Pox, Twilight mentions that she had been reading about "unusual equine illnesses" in a book entitled 'Perplexing Pony Plagues'. One of the illnesses she mentions is Hay Fever, though she gives no details about it.

Love poisoning
A love potion is created in Hearts and Hooves Day by the Cutie Mark Crusaders and administered to Cheerilee and Big McIntosh. The Crusaders borrow a book from Twilight and use a recipe from it to create a love potion, mixing "a tuft of cloud" and "a bright rainbow's glow", and stirring with a Pegasus feather. They let Cheerilee and Big McIntosh drink it, and the two become helplessly in love with each other. The Crusaders later discover that the drink makes ponies so lost in each other's eyes that they can't do anything else, and that the antidote is to keep the affected ponies "from looking into each others eyes for one full hour", which they succeed in doing, and the spell is broken.

Petrification
A cockatrice petrifies Twilight Sparkle and some chickens in the episode Stare Master. Fluttershy tries to warn the Cutie Mark Crusaders to "never look one in the eye. If you look a cockatrice in the eye–", but she is cut off; later she confronts the cockatrice, which manages to partially turn her into stone, but through her own powerful stare she commands the cockatrice to turn Twilight and the chicken back to normal, and the stone that was partially encasing her shatters.

At the beginning of the episode The Return of Harmony Part 1, Discord, having been turned to stone by Princess Celestia and Princess Luna using the Elements of Harmony long beforehand, escapes after the Cutie Mark Crusaders get into a fight in front of his stone form. Celestia explains that the spell to keep Discord contained broke due to her and Luna no longer being connected to the Elements. At the end of the episode The Return of Harmony Part 2, the six main ponies use the Elements to turn Discord back to stone.

Poison joke
Poison joke, which appears in the episode Bridle Gossip, is a magical plant that causes ridicule-inducing afflictions on the six main ponies who come into contact with it.

In the episode, the ponies accidentally stumble into a large patch of poison joke despite warnings from Zecora, which are misconstrued as threats. The plant has large leaves with a multi-petaled bulb sticking out of the center, each bulb sporting a few stamen. The entire plant is blue, including leaves and stalk, with dark streaks running over it in a design.

Like its namesake, poison oak, it affects the ponies after they merely come into contact with it, but as described by Zecora, the plant does not poison its victims; rather, it plays practical jokes, which manifest as physical afflictions. The jokes in the episode magically match the victim's personality and traits.

In the episode, the ponies are afflicted with the following:
 * Twilight Sparkle's horn becomes limp and covered in blue spots.
 * Rainbow Dash's wings become inverted, being upside down and on her stomach area, impeding her flight.
 * Applejack shrinks down to a tiny size and can fit on a pony's hoof.
 * Rarity's mane, coat, and tail become frizzled, very long, and mop-like.
 * Pinkie Pie's tongue becomes swollen and covered in blue spots, making her speak unintelligibly.
 * Fluttershy's voice deepens into that of a stallion with a deep voice, provided by Blu Mankuma.

The effects of poison joke are eventually cured when the ponies take an herbal bath for which the recipe is found in a book called Supernaturals: Natural Remedies and Cure-Alls That Are Simply Super, which Twilight initially ignored in the episode because of the first part of its title.Twilight told Spike when she saw that book ,"Spike,that book is just a load of hooey!" But that book did contain the cure!

Allergies
During the episode Bridle Gossip one of the possible causes Twilight Sparkle considers to explain what turns out to be the effect of poison joke is an allergic reaction.

Pony pox
Fluttershy pretends to be afflicted with pony pox in Hurricane Fluttershy in an attempt to avoid Rainbow Dash's recruitment efforts toward setting a new tornado speed record. Fluttershy's faked symptoms include sneezing, coughing, and being covered in red spots. Rainbow Dash "cures" Fluttershy by dousing her with water, causing the fake red spots to wash off.

Corruption due to the Alicorn Amulet
The Alicorn Amulet in Magic Duel blesses the wearer with enhanced magical powers but also "corrupts" the user, according to a book that the main characters find. Trixie, who possesses the amulet and uses it to take control of Ponyville, becomes more and more tyrannical and bitter as she continues to rely on its power. Since the amulet has a lock that prevents anyone other than the user from taking it off, Twilight Sparkle tricks Trixie into removing the Alicorn Amulet by pretending she possesses an even stronger amulet. Trixie's horn's aura, which was red before, turns back to pink, and her eyes no longer glow red from the influence of the amulet.

Sombra's curse/Shadow poisoning
In The Crystal Empire - Part 1, Shining Armor escapes from Sombra's attack at the cost of having shadow crystals being grown on his horn which nullify the use of unicorn Magic. It's only when the magic of the Crystal Heart is restored that Shining Armor is cured.

The trots
In The Cutie Pox, Twilight mentions that she had been reading about "unusual equine illnesses" in a book entitled 'Perplexing Pony Plagues'. One of the illnesses she mentions is "the trots".

Gigantism
The Sparkle World story The Hero of Ponyville! involves Spike becoming gigantic; however, unlike what transpires in the episodes The Cutie Mark Chronicles and Secret of My Excess, Spike possesses his usual appearance, though on a larger scale. Twilight Sparkle refers to him as a "giant baby dragon" and attributes his enlargement to him brushing against a magic plant. Later in the story, Twilight bathes him with a magic cure and he shrinks to normal size.

Paralysis
In one of the German comics, Twilight Sparkle, Applejack, and Spike discover Pinkie Pie and Fluttershy appearing to be petrified. Twilight reads in a book that when ponies are looking forward to something so much that they can't take the anticipation, they might get paralyzed. She tells Applejack and Spike that the cure is a special cereal with a smell that calms them down so they can wake up, and that this cereal doesn't grow anywhere in Equestria, only being found beyond the Everfree Forest. After traveling to a barley field outside of Equestria, the three of them return to Ponyville with some of the barley and make a campfire with it, which wakes up the paralyzed ponies.