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Do we know how long potions (in general, or at least specific ones) are potent (no pun intended) in Harry Potter canon?

E.g. do they last a couple of hours? Minutes? Years?

I seem to vaguely remember some comments of Snape's about Wolfesbane potion therfore I think at least some information exists.

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    I don't recall precisely, but I think Snape was brewing the Wolfsbane potion for Lupin every month. That suggests that it likely has a short period of effectiveness. – Anthony Grist Aug 31 '12 at 19:18
  • @AnthonyGrist - I was thinking more along the lines of "you need to drink this ASAP" comment that I seem to vaguely recall – DVK-on-Ahch-To Aug 31 '12 at 19:20
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Polyjuice Potion seems to last at least 8-12 hours (I think this is obvious, but I'm just going by canon). In Chamber of Secrets in chapter 12, The Polyjuice Potion, Hermione is up "very early" on Christmas morning, adding lacewing flies to the Polyjuice. She suggests that the trio take the Polyjuice that night, which, depending how early she was up in the morning, gives the 8-12 hour window, give or take. And I think the events of Goblet of Fire probably demonstrate that Polyjuice has a decent shelf life. It would be hard to consume an entire cauldron of Polyjuice super quickly (although Polyjuice has to be drunk on the hour for ongoing effects.). In chapter 21, The Unknowable Room, in Half-Blood Prince, in March, Harry suspects Draco Malfoy of having stolen Polyjuice Potion from Slughorn on the first day of classes the past September. We subsequently learn that Draco has been giving Crabbe and Goyle Polyjuice Potion so they can act as Malfoy's lookouts while he works on the cabinet in the Room of Requirement. So altogether that gives a window of 8-12 hours to 5-6 months minimum shelf life.

Veritaserum is another potion that could have a solid shelf life. In Goblet of Fire, chapter 27, Padfoot Returns, when Snape threatens Harry with Veritaserum, he mentions the use of Veritaserum is highly regulated by the Ministry of Magic. This could be interpreted as the Ministry controlling most supplies of Veritaserum and doling them out when appropriate. Moreover, the events of Order of the Phoenix suggest Delores Umbridge used Veritaserum on students throughout the course of an entire school year, or close to it. As Veritaserum is not a fast-brewing potion, Snape had to have stores of it. Snape says to Umbridge that she used up all his stores of Veritaserum. So I estimate Veritaserum has a shelf life of at least ten months (the length of a school year in Harry Potter)

Hermione notes in chapter 15, The Unbreakable Vow, in Half-Blood Prince, that there are at least one dozen different love potions. As they all are being sent from Weasleys' Wizarding Wheezes, I imagine their shelf life is good and, as TGnat and NominSim both first mentioned, strengthen as they age. I believe Amortentia has a pretty strong shelf life as well, as the Love Room in the Department of Mysteries has a large fountain inside that flows with Amortentia [POTTERCAST TRANSCRIPT] Now, volume wise, that would be a lot of potion. It would seem impractical to have a fountain flowing with a potion the Unspeakables would have to brew super frequently.

It seems clear that Felix Felicis has a shelf life of at least 9-10 months, as Harry wins this potion on the first day of classes in September and takes it the following June.

Has anyone mentioned the Horcrux potion in the sea cave? Clearly this potion has an incredibly long shelf life. It's unclear whether the Horcrux potion is a regular potion or if it would be considered of the Dark Arts. In What Order Were the Horcruxes Made In, I estimated that Voldemort created the Slytherin locket Horcrux between 1945 and 1946. Deathly Hallows shows Voldemort putting the locket in the potion basin in 1978, when Regulus Black was seventeen. Regulus drank the potion in 1978. Somehow the basin was refilled with potion, which sat untouched for nineteen years until Dumbledore drank it in June of 1997. So we know the Horcrux potion has a shelf life of at least nineteen years.

Wolfsbane seems to have a shelf life of at least 1-7 days. In Prisoner of Azkaban, Lupin explains that he drinks Wolfsbane in the week prior to the full moon. In Half-Blood Prince, he confirms that Snape did indeed brew the Wolfsbane potion for him every month. So I suppose it couldn't last longer than however many days are in a complete moon cycle, but it must last long enough for the werewolf to drink it during any of the seven days preceding the full moon.

‘The Potion that Professor Snape has been making for me is a very recent discovery. It makes me safe, you see. As long as I take it in the week preceding the full moon, I keep my mind when I transform ... I am able to curl up in my office, a harmless wolf, and wait for the moon to wane again.

Prisoner of Azkaban - page 258 - Bloomsbury - chapter 18, Moony, Wormtail, Padfoot and Prongs

‘But I do not forget that during the year I taught at Hogwarts, Severus made the Wolfsbane Potion for me every month, made it perfectly, so that I did not have to suffer as I usually do at the full moon.’

Half-Blood Prince - page 312 - Bloomsbury - chapter 16, A Very Frosty Christmas

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    I don't think Draco would have been able to steal anywhere near enough Polyjuice Potion in one lesson to support transforming Crabbe and Goyle for the entire year. Considering he has the previous Potions teacher sworn to assist him, it seems more likely that it came from Snape. – Anthony Grist Aug 31 '12 at 19:16
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    I also disagree with your points about the Horcrux potion. Regulus Black would have had to consume the entire potion in order to steal the locket, which seems to suggest that the basin refills itself after some period (though not immediately); that probably means there's some Dark Arts involved. Also, given Regulus's age (born in 1961) and the fact that he was the one to offer Kreacher to Voldemort to test the defences in the cave, it seems likely that Voldemort hid the horcrux considerably later than the mid-1940s. – Anthony Grist Aug 31 '12 at 19:28
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    Kreacher also drank the Horcrux potion. Anyhow, yes, I checked DH and Voldemort indeed put the locket in the basin while Kreacher and Regulus were with him in the sea cave, when Regulus was 17, and he refilled the basin with potion manually. That would've been in 1978. Shortly thereafter, Regulus drank the potion, Kreacher switched the lockets, and Regulus died in the sea cave. It's here that I don't know how the basin refilled. You're right -- it's not 52 years. It's 19 years. But 19 years is also quite a nice long shelf life. Thanks for pointing that out to me. :) – Slytherincess Aug 31 '12 at 22:38
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    @AnthonyGrist -- Draco refused to tell Snape what he was doing during the events of Half-Blood Prince and completely shut him out. When Snape offered to help him, Draco was adamant about going it alone. See The Unbreakable Vow in HBP. We could just as easily say it would've been impossible for Slughorn to have had Felix Felicis on the first day of classes, as it takes six months to brew, as we can say that Draco didn't get Polyjuice from Slughorn. It's possible that he did. :) – Slytherincess Aug 31 '12 at 23:25
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In HBP Slughorn implies that love potions have a shelf life:

"Was this potion within date?" asked Slughorn, now eyeing Ron with professional interest. "They can strengthen, you know, the longer they're kept."

While not a specific answer it does indicate that some potions can go bad.

  • +1 Some might consider a love potion getting stronger to be a good thing too. – NominSim Aug 31 '12 at 15:43
  • +1 for great catch, especially since the question arose as part of fuguring out Slytherincess' Merope question which dealt specifically with love potions. But I fully agree with NominSim's comment - this would be a "good" thing for such a potion to expire, had I wanted to use one :) – DVK-on-Ahch-To Aug 31 '12 at 15:50
  • @DVK-on-Ahch sorry for being a necromancer here but i'm sure you wouldn't, you can love someone to the point you never let them out of your sight, track everywhere they go, stalk everyone they ever speak to through paranoia, even get physically violent through jealously and kill to protect whats 'yours'. Love can turn into a nightmare when it goes too far. Expiration in this case would just mean its far far to strong to use unless you wanted to turn the relationship into a living hell. Stronger isn't always good when it comes to emotions – Matt Jun 21 at 20:08
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I think it depends on the potion, and there isn't really a lot of canon evidence toward specific time periods. As TGnat's answer points out, love potions get stronger with time.

Felix Felicis seems to be able to keep for a long period of time, as evidenced by both the length of time that Harry keeps his without it going bad, as well as the lack of any sort of warning from Slughorn as far as an expiration date on the potion. (One would assume that if it were to go bad in say 6 months, that Slughorn would tell Harry when he gave it to him.)

Further evidence towards certain potions at least lasting quite a while can be had during the same chapter in The Half Blood Prince. Slughorn shows the students several very powerful/difficult potions (Polyjuice Potion, Amortentia, Veritaserum, and Felix Felicis). We can assume that since these potions are said to be very difficult to make, that Slughorn likely wouldn't have brewed them all simply to show the class and then discard them. Indeed during The Order of the Phoenix Snape tells Umbridge that she has "run through his store" of Veritaserum. So he at least keeps some in storage for a certain period of time.

This of course is all supposition, since the only canon evidence of potions going "bad" seems to be Slughorn's quote in The Half Blood Prince:

"Was this potion within date?" asked Slughorn, now eyeing Ron with professional interest. "They can strengthen, you know, the longer they're kept."

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With regard specifically to the Wolfsbane potion, I'd estimate that its shelf life is no more than two lunar cycles (one lunar cycle is roughly twenty-nine and a half days), and possibly as short as one lunar cycle.

After admitting to Harry, Ron and Hermione that he's a werewolf (Chapter 18), Lupin says that he's safe as long as he takes the potion in the week preceding the full moon:

The potion that Professor Snape has been making for me is a very recent discovery. It makes me safe, you see. As long as I take it in the week preceding the full moon, I keep my mind when I transform… I’m able to curl up in my office, a harmless wolf, and wait for the moon to wane again.

That could be interpreted as only needing to be taken once in the week prior to the full moon. However, in chapter 8, when Harry is in Lupin's office and Snape delivers the potion, there's this exchange:

“Fascinating,” said Snape, without looking at it. “You should drink that directly, Lupin.”

“Yes, Yes, I will,” said Lupin.

“I made an entire cauldronful,” Snape continued. “If you need more.”

“I should probably have some again tomorrow. Thanks very much, Severus.”

Snape saying that Lupin should drink it directly suggests that there's a limited period in which it's effective. However, if it lasted less than a day Snape is unlikely to make an entire cauldronful because most of it would be wasted. And, since Lupin says that he should probably have some again tomorrow, it seems to indicate that the potion is required more than once prior to the full moon to make the transformation safe.

Chapter eight occurs at the end of October (Halloween), and the next mention of Lupin being "ill" is Christmas - roughly two full moons later - when Dumbledore asks "Severus, you’ve made the potion for him again?”, which suggests to me that it doesn't store for periods longer than that.

  • I read “You should drink that directly, Lupin.” as "it is most effective right away, but still works later though not as good" – DVK-on-Ahch-To Sep 1 '12 at 0:06
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    An option not considered is how it is stored. For example cow milk stays good for quite a long time while vacuum, but if you open the package you have to drink it in a few days. The wolfsbane potion could be similar. It would explain the cauldronful, as Snape would then have a way of conserving that, but the potion in the cup could turn bad very quickly. – 11684 Sep 15 '13 at 14:26
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To add a few points to the existing answers:

Polyjuice Potion

In the beginning of Deathly Hallows Hermione mentions that she stole Moody's supply of Polyjuice Potion:

not to mention smuggling Mad-Eye's whole stock of Polyjuice Potion right under Ron's mum's nose.

Some ten months later they use up the last of it when they raid Gringotts:

"There's really only enough left for one of us," said Hermione, tilting the thick mudlike potion against the lamplight.

So the potion must last at least that long, and perhaps even longer since we don't know when Moody actually brewed it.

Snape's Riddle Potions

In Philosopher's Stone one of the protections for the philosopher's stone was Snape's potions challenge. We can assume that Snape was not periodically going down there to replace the potion, as he did not even know how to get past Fluffy. If that is the case then the potions must have lasted from when they were first put in place until the end of the year when Harry and Hermione used them, and perhaps even indefinitely. However, this is not necessarily a proof, because one could argue that it is possible for the potions to be replenished/replaced remotely.

Veritaserum

In Goblet of Fire when Snape brings the Veritaserum to Dumbledore it is described as:

Snape handed Dumbledore a small glass bottle of completely clear liquid: the Veritaserum with which he had threatened Harry in class.

A strict literal reading of this could indicate that it is the very same bottle that Snape threatened Harry with, in which case the potion had lasted at least three months. But, again, this is not necessarily a proof because one can argue that the above quote just means that it was the same potion, but not that it was the very same sample of that potion.

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