Felix Felicis
Potion information

Effect
Increases the luck of the drinker

Side-effects
Overuse can cause giddiness and reckless behaviour
Extremely toxic in large quantities
Highly disastrous to brew incorrectly
Characteristics
Molten gold in colour
Droplets leap like goldfish above potion's surface when in cauldron

Brewing time
Six months

Difficulty level
Advanced
Known ingredients
Ashwinder egg
Squill bulb
Murtlap tentacle
Tincture of thyme
Occamy eggshell
Powdered common rue

Inventor(s)
Zygmunt Budge

"Mine own invention, my masterpiece; the crowning achievement of my career. Bottled good fortune. Brewed correctly the drinker of this potion will be lucky in all their endeavours, but be warned … excessive consumption is highly toxic and can cause extreme recklessness. Fans of Quidditch were quick to protest that a potion which gives the drinker good luck was hardly fair and use of my potion was banned, quite rightly, from all competitive events … except potion-making tournaments."
—Zygmunt Budge

Felix Felicis, also called "Liquid Luck", is a magical potion that makes the drinker lucky for a period of time, during which everything they attempt will be successful.

It is meant to be used sparingly, however, as it causes giddiness, recklessness, and dangerous overconfidence if taken in excess. Felix is highly toxic in large quantities and is also a banned substance in all organised competitions, such as Quidditch, along with all other methods of cheating. It is very difficult to make, disastrous if made wrong, and requires six months to stew before it is ready to be consumed.

Recipe
Add Ashwinder egg to a cauldron, then add horseradish and heat.
Juice a squill bulb, add to the cauldron and stir vigorously.
Chop up anemone-like growth on the back of Murtlap, add to mixture and heat.
Add a dash of tincture of thyme and stir slowly.
Grind up Occamy eggshell and add to mixture.
Stir slowly then heat the cauldron.
Add a sprinkle of powdered common rue.
Stir vigorously then heat the cauldron one last time.
Wave wand over potion in a figure of eight and say incantation ‘Felixempra!’

Effects
"Felix Felicis is liquid luck, which makes the person who drinks it lucky for a certain period of time."
—Description of the effects of the potion

Felix Felicis causes the drinker to have a limited period of good luck, during which they are likely to to succeed in all endeavours in which success is possible. They have a strong perception of this effect, including a high level of confidence and a "sensation of infinite opportunity." This is accomplished not through direct application of force or granting the drinker any extraordinary powers, but by inspiring the drinker with a favourable pathway through the circumstances. When Harry took the potion, he had the sensation that 'Felix' knew what it was doing and that he needed only follow its inspiration, however unlikely the approach seemed as a means of accomplishing his goal. It indeed led him into a near-freakish but plausible set of circumstances in which all the right choices seemed obvious to him. Along the way, without even meaning to, he also accomplished some minor side goals, such as breaking up Ron's bad relationship, and destabilising Ginny's relationship with Dean to give Harry more of a chance.

A person under the potion's inspiration would likely prove highly adaptable to any unexpected change in the circumstances. There are always infinite possibilities in any situation, some of which doubtless lead to the desired outcome, and Felix can highlight them no matter what happens.

Though Felix Felicis confers no extra powers on the user, it seems capable of drawing out the best reserves of their ability if needed. Harry was able to use Refilling Charms non-verbally, even though he had not yet managed it in his previous classroom practise.

There is a period of 'coming down' when Felix Felicis wears off. During this time, the user's sense of confidence fades, and unlucky circumstances can quickly catch up to them if they are not vigilant. It is unclear whether Felix wearing off actually increases the user's bad luck in a small overbalancing period (though obviously not so great as to undo whatever they have just accomplished), or whether the user simply keenly perceives the return of 'ordinary' levels of luck and all the subsequent challenges and dangers.

Limitations
"Luck can only get you so far, Harry... Luck is not powerful enough to get through a powerful incantation."
—Hermione Granger explaining to Harry Potter the limits of the luck induced by the potion

As Hermione pointed out, the potion is not able to better the chances of the drinker against particularly powerful enchantments, since members of the D.A. were not able to bypass the Peruvian Instant Darkness Powder that Draco Malfoy used. Hermione also claimed that Harry's usage of the potion to help discover what Draco was up to in the Room of Requirement would be a waste, as the Room was too powerful for the potion to help penetrate.

The potion's effectiveness seems to wane after a certain amount of time, as it did in Harry Potter's situation when he made his way back to the Gryffindor Common Room and he ran into Peeves, but was only just barely able to dodge him with the potion's influence.

Overdosing is dangerous, as it is very toxic in large quantity, and over-reliance on it may lead to dangerous overconfidence, giddiness, and recklessness. The potion is very difficult and time-consuming to brew, and disastrous if concocted incorrectly. Due to its effects, it is considered a tool of cheating and therefore prohibited in organised events such as Quidditch and examinations.