Misc drug half life + a calculator

[emkee_reinvented]

Edit: seems hardly credible, will leave it up as warning for the time being

https://halflifedb.co/drugs/

Just found this but is this useful. Credible ? seem like a sort of tool.

 

[placebonaut]

I can see it being useful as a rough calc.

would have liked to see ranges rather than mean half life given drugs effect people differently.

Also GBL is just wrong I think given it's rapidly converted into GHB.

 

[notsmokeymcpot42088]

^GBL is indeed converted to GHB. It is a prodrug and I am not positive how much or how safe that conversion is in vivo though.....other ppl may.

For that reason I trust GBL less than GHB --- and the increased potency and risk of OD

As long as it works I see it as a good tool -- it would be cool if you could plug your own halflife in beteen a range or somethin but still -- they got MG as the unit of measurement for alcohol that isn't ideal.....Mg for GBL is a weird one too, ML's right? Or am I thinkin of 1.4?

 

[placebonaut]

^GBL is indeed converted to GHB. It is a prodrug and I am not positive how much or how safe that conversion is in vivo though.....other ppl may.

For that reason I trust GBL less than GHB --- and the increased potency and risk of OD

As long as it works I see it as a good tool -- it would be cool if you could plug your own halflife in beteen a range or somethin but still -- they got MG as the unit of measurement for alcohol that isn't ideal.....Mg for GBL is a weird one too, ML's right? Or am I thinkin of 1.4?

plugging in your own half life would be good for the experienced, however body chem + subjective view will = confused answer for the inexperienced.

having said that I'm not sure an inexperienced person would find this as useful as the well practiced.

you're right on GBL, should be ml.

guess the other issue with this as well is that strength plays a part, no-doubt much (if not all?) of this is based on "pure" drugs given the random few I clicked on are all using .gov type sources

 

[emkee_reinvented]

1 ml GBL is ~1.6 GHB [when needed correct to lazy to search]

Wonder how they come to the conversion to mg. But using their tool,
1.6 gr GBL ingested 6 hour later:
Now estimated in body: 25.00 mg(1.6% of starting amount)
Half-life used: 0.5 h

So doing that with GHB also 1.6 gr:
Now estimated in body: 6.25 mg(0.4% of starting amount)
Half-life used: 0.8 h

Found this when looking for the halflive of Cocaethylene which isnt mentioned. Neither the Cocaine & Alcohol combination forming it. But the one for Cocaine feels off to.

Cocaine
Educational first-order elimination curve using an approximate half-life estimate. This is not medical advice and does not predict impairment or laboratory outcomes.

Category: stimulant · Updated: 2026-01-18

Dose taken
500mg
Time since dose (hours)
4 hours
Now estimated in body: 31.25 mg
(6.3% of starting amount)Half-life used: 1.0 h

Think it s safe to assume seeing the nebula how they get to all this. They do link to NBCI but that didn t explain to me how they convert GBL from ml. to mg or gram units. And the lack of insight it gives makes it useless. No clue how they got the 31.25 mg. regarding Coke

Not gonna try. Sound s recless/ dangerous assuming this, enough to maybe delete or keep it up at best as a warning to never trust these. Without some confirmation of a knowledgeable 3rd party. Thank s for the input @placebonaut & @notsmokeymcpot42088 [it claim s updated 2026 but i wouldn t trust it]

 

[chippermonk]

I've never really understood just what half life means in practical terms. The half- life is the point at which your body eliminates half the drug, but it isn't the case that you are now half as high. The effects decline much quicker obviously. Why is that and what is the practical use in this knowledge? I understand that drugs with shorter half lives induce withdrawal quicker. Kratom at 23 hours gives you a lot more leeway with withdrawal than conventional opiates. But fentanyl has a 7 hour half life, much longer than most opioids, whereas as heroin has one of .1 hours( 6 frickin minutes?!!). Hell, that doesn't even remotely correspond to length of high, nor does 23 hours for kratom.
Anyhow, I'm just asking for explanation. Thanks.

 

[chippermonk]

...well, a little bit of reading up explains some of that question. For example, the drug may move out of the brain to other areas where it has no effect, so it's still in the body but not in an area where it has a psychoactive effect, or it may be metabolized into a form that has no psychoactive effect. Even more interesting ( and something I'm curious about) the brain receptors may become desensitized or saturated, meaning the drug just doesn't have much of an effect anymore. Which also explains why you can keep redosing without getting as much desirable effect.
Still don't see how that .1 hour half life from heroin shown in the table would work though. I guess that's a ROA issue: if you inject then yeah, short rush, short effect. Different ROA, different half life?

 

[placebonaut]

I've never really understood just what half life means in practical terms.

helps with dosing timing depending on the drug e.g. if you normally take 10mg with a 24 hour half life, if you were to take another 10 at T + 24 hours then you would have 15mg in your system (though it's not quite this straight forward depending on the drug and how it's metabolized etc.)

This also plays a factor in toxicity and side effects

not really read about this but in my head logically I would guess it might also play a part in withdrawal effects

I can see half life awareness being a useful tool to help manage and prevent too high dosing, and therefore over dosing esp. with CNS depressants for example, but I wouldn't be trusting my life on a calculator that knows nothing about my body or how the drugs are affecting it!

 

[emkee_reinvented]

The initial search was a bit to give a estimate on how long one would suffer from doing a lot of Alcohol and a fairly amount of Cocaine. To get a general idea Coke purity and active cut s not even in calculated. But it was useless. In this case it would have been a good indicator for what kinda trouble you are in. A might be unintentional overdoing.

If you snort 1/ 2 gram. Been 2 decades ago that i used it but never in these quantity s. At 4 hour s only 31.25 mg remains without mentioning purity/ ROA/ co factors involved.
Personally after that dose having a 'how much was in a OG Coca-Cola ?' in you. Seem s un-lightly. Not a great find or tool

GHB/ GBL immediately catched attention on here. Had no time to check att. Was just looking for some sort of timeline. To give a rough estimate how long it would last. Maybe get medical help.

You all three kinda point out the obvious not a credible tool. The number s don t match and it lack s some back up on how the get to it. Source s, ROA s and combos all relevant

 

[chippermonk]

I think it can be a useful tool but it's definitely complicated. It's clear to me that there is a distinction between still having half the amount of drug left in your system and having half the high. And if you don't have the half the high, then how would adding more drug cause you to OD or get much more high? The drug may be still in your system, in some form, but it isn't still giving you the original drug effect.
Now is it still fucking with your liver or occupying brain neurotransmitters such that you can't get as good a high as your first dose? That could well be. Probably smart to not redose until you are past the half- life at a minimum. A simple example is coffee: my first cup or two of the day is awesome but additional cups for the rest of the day never do anything for me except make me kind of anxious and unpleasantly wired. But if I wait til the next day, I'm back to enjoying it...of course maybe that's partly just because it's relieving my withdrawal Anyhow, I have to get past the half life, I would guess.

 

[chippermonk]

TL;DR. Don't mind me, my mind is wandering

 

[placebonaut]

I think it can be a useful tool but it's definitely complicated. It's clear to me that there is a distinction between still having half the amount of drug left in your system and having half the high. And if you don't have the half the high, then how would adding more drug cause you to OD or get much more high? The drug may be still in your system, in some form, but it isn't still giving you the original drug effect.
Now is it still fucking with your liver or occupying brain neurotransmitters such that you can't get as good a high as your first dose? That could well be. Probably smart to not redose until you are past the half- life at a minimum. A simple example is coffee: my first cup or two of the day is awesome but additional cups for the rest of the day never do anything for me except make me kind of anxious and unpleasantly wired. But if I wait til the next day, I'm back to enjoying it...of course maybe that's partly just because it's relieving my withdrawal Anyhow, I have to get past the half life, I would guess.

tolerance is another very good point! some drugs will build it very quickly with consecutive days usage, and it will reset differently depending what's being taken and gap since last usage. Factor in half-life, biology, combos etc, and all the half life calc is doing is providing you more info to help make a more informed decision, it's not going to be keeping you safe on it's own

 

[JackARoe]

I think it can be a useful tool but it's definitely complicated. It's clear to me that there is a distinction between still having half the amount of drug left in your system and having half the high. And if you don't have the half the high, then how would adding more drug cause you to OD or get much more high? The drug may be still in your system, in some form, but it isn't still giving you the original drug effect.

Yeah I am sill looking for a detailed thread in N&PD. I keep looking but still can't find it. A lot of explanations on the differences between half life and length of drug effects. I should have booked mark it as it was some years back.

I can see half life awareness being a useful tool to help manage and prevent too high dosing, and therefore over dosing esp. with CNS depressants for example, but I wouldn't be trusting my life on a calculator that knows nothing about my body or how the drugs are affecting it!

We would think it is straight forward. But can get confusing. We hear of diazepam having many hours of half life, then the metabolites can go on a many hours too. Yet most people I speak to claim diazepam only last them 4-6 hours regardless of metabolites. Now I have no tolerance and can feel diazepam in my system for 2 days after I take it. I stay a little sedated the day or two following. But I think for people that have high tolerance and dependence the longer half life helps only so much.

Gabapentin confused me too, I can feel it into the next morning when I take 1800 mgs the night before. Yet it is said to have a very short half life, not more than 5-7 hours at max. It was that notion that made the thread in N&PD interesting, some knowledgeable people explaining the differences.

I will keep looking for that thread.

 

[HeadphonesandLSD]

I've never really understood just what half life means in practical terms.

It's indeed the time it takes for the body to eliminate half of the drug. But it doesn't work like most people think.

If a drug has a 2 hour half life then;

00:00 hours - Consume 10mg
02:00 hours - Body eliminates half (5mg) so there is now 5mg floating around in the system
04:00 hours - There are now 2.5mg floating around in the system
06:00 hours - There are now 1.25mg floating around in the system
etc. etc.

The reason it's useful is because half life and duration are kind of tied together. In the above example the first two hours would be the "peak" (after the drug itself takes effect of course). 2 hours later you'd start to "come down". 4 hours later you might not feel like you're on the drug anymore but there is still 1/4th of it floating around in the system. The next day a tiny tiny bit may remain. Enough to be detected on a drug screen probably.

Shorter half life usually means quicker onset and duration. But the effects of a drug on any given person are subjective of course and there are some oddballs out there. It's useful information to know because there can be big differences in half lives even with closely related drugs. For example, 2C-B have a 1.5-2.5 half life. Short acting drug. Can take it and most likely be normal enough tomorrow to go into work or do whatever you need to do around sober people. 2C-G has an 18-30 hour half life. Take it tonight and you'll still be feeling strong effects 12 hours from now and maybe even 24 hours from now. Maybe even still feel like you're on the peak (I did). The flip side: 2C-B has a pretty fast onset as you'd expect from most other drugs. Where 2C-G can take 3-4 hours before you even start to feel first alerts (at least that's how it was for me).

Take xanax vs. valium. Xanax has a very short half life which makes it more addictive and makes withdrawal feel more extreme if you've been taking it everyday (or multiple times a day) for awhile. Valium on the other hand has a very long half life but the onset is a bit slower than xanax (but not as slow as something like 2C-G, even though the half lives are comparable). Assuming someone is addicted to xanax and wants to quit replacing xanax with valium for a week or two then tapering the valium slowly will provide a much nicer time than attempting to taper xanax. Since xanax's halflife is so short it requires multiple doses over a night/day to keep the levels in the system high enough to starve off withdrawals. Valium on the other hand can be taken at say 8pm and you can be pretty sure that you'll sleep all night peacefully without waking up in withdrawal. It will still be in your system the next morning doing its thing.

As far as this calculator. I would not rely on it. Since some drugs (like 2C-G above) have highly variable half lives depending on what organism is taking the substance. Most of the quoted half lives are from testing done on rats, monkeys, mice and other lab animals. Sometimes you'll get some solid numbers from human testing. But many substances in common use haven't had human testing yet. Then there is the issue that half lives can widely vary depending on what kind of human you're giving the substance to. Even two people from the same race can have varied results depending on how their liver processes the substance or how the substance is injested (e.g. orally, nasal, IV, and IM).

Your best bet is to use a resource like erowid to check for known half life. If it isn't listed there search for papers on scihub. Then do some quick math yourself with a calculator to get an idea of how the half life is for whatever substance you're taking. From there slowly test the substance yourself and see how it personally affects you.

Also half lives aren't always tied directly to peak effects of drugs. But they're a pretty helpful rule of thumb to go by if you're unfamiliar with a substance. This is where reading trip reports comes in. Reading multiple trip reports (hopefully with timelines) will give you a general idea of how the substance affects the average person. Unless a substance is really really new usually there are at least a few reports floating around. If not and you're not willing to be everyone else's lab rat then you should hold off and wait until some appear or papers pop up in the journals.

 

[HeadphonesandLSD]

Gabapentin confused me too, I can feel it into the next morning when I take 1800 mgs the night before. Yet it is said to have a very short half life, not more than 5-7 hours at max. It was that notion that made the thread in N&PD interesting, some knowledgeable people explaining the differences.

I will keep looking for that thread.

Just because the substance has passed through the system doesn't mean the effects it had on the brain itself have passed. It can take the brain (and body) a long time to adjust to the absence of the substance after it has been eliminated.

This is why withdrawal exists. Since consuming a substance often changes how the body itself produces and interacts with natural endorphins (and other stuff).

Think of it like driving a car through a farmer's field. You come racing through at high speed spinning tires and busting through fences. The car passes through in a matter of seconds. But it takes the farmer many days to repair all the damage it might have caused. It takes even longer before the livestock go back to their normal routine after you've spooked them and they ran away.

 

[JackARoe]

Just because the substance has passed through the system doesn't mean the effects it had on the brain itself have passed. It can take the brain (and body) a long time to adjust to the absence of the substance after it has been eliminated.

I would imagine the opposite exists too. How can some people tell me (family members trying to taper) that their 40 mgs of diazepam only holds them for a few hours when we are told the metabolites can last 100 hours? After some research here I learned that just because a drug is in the body does not mean it is hitting the receptors like the first few hours. And now the opposite can be true as drugs can trigger reactions in the brain that last longer than the main effects, even after it is cleared.

Think of it like driving a car through a farmer's field. You come racing through at high speed spinning tires and busting through fences. The car passes through in a matter of seconds. But it takes the farmer many days to repair all the damage it might have caused. It takes even longer before the livestock go back to their normal routine after you've spooked them and they ran away.

I like that! Sort of explains many addictions. And many people here go crashing through without consideration for damage and then come here to BL in pain for answers, after the fact, on the cleanup they have to do. Meanwhile others drive carefully and try not to create muddy tracks they have to clean up by being cautious and following some rules of the game.

I really need to find that post in N&PD.