Caffeine

Dosage:

[dose/(0.7•m)] formula for mg/L

KD is 0.466 mg/L (at the adenosine A2a receptor)
KD at the adenosine receptor A1 is 2.33 mg/L
adenosine A2B receptor: 2.53
and adenosine A3 receptor is 15.54 mg/L
1.4 mg/kg Can possibly lead to insomnia
2 mg/kg Delays fatigue & increases alertness

3 mg/kg Causes relaxing effect, with elevated mood
4 mg/L increases Serotonin 20% above baseline
10 mg/kg-30 mg/kg increases dopamine by 100-125 units

13 mg/L blocks 50% adenosine

5 mg/kg Increase Norepinephrine. Increase Epinephrine by 50%.
6 mg/kg Safe-limit
7 mg/kg to inhibit the release of GABA & cause euphoria.
9 mg/kg to increase Epinephrine levels by 100% above baseline.

800 mg increases cortisol by 52% (+/- 44%)

800 mg increases testosterone by 21% (+/- 24%)

Exercise increases testosterone by 15% (+/- 19%)
It takes about 10 mg/kg to cause panic attacks, also increases Glutamate by 50 units
15 mg/kg can cause twitching and vomiting and even psychotic delirium with full recovery in 6 hours
15 mg/L is the mild toxic dose eg: nervousness, irritability, and potential nausea, palpitations, tremors, perspiration, paresthesia.
80 mg/kg causes unconsciousness
2 g (30 mg/kg) usually results in hospitalization
Toxic dose 50 mg/L
LD50 187 mg/L
Highest dose ever survived 50 g
187±96 (LD50±SD)
LD100 567 mg/L
LD50 in rats: 192 mg/kg
Caffeine anxiety LOAEL 9 mg/kg
Caffeine anxiety NOAEL 3 mg/kg
Caffeine headaches LOAEL 6 mg/kg
Caffeine headaches NOAEL 3 mg/kg
Caffeine insomnia LOAEL 6 mg/kg
Caffeine insomnia NOAEL 3 mg/kg
400 mg reaches steady state in 18 hours (3 half-lives)
The lowest dose to ever cause death was 3,600 mg
EC50 551±81 micromole
Coffee:
Robusta beans are 2.7% caffeine, while Arabica beans are 1.5% of caffeine

Dunkin' Donuts Coffee (s, m, l, xl) = 180 mg, 210 mg, 270 mg, 330 mg 

Dunkin' Donuts Frozen Coffee (s, m, l): 196 mg, 295 mg, 393 mg

Dunkin' Donuts Iced Coffee (s, m, l): 198 mg, 297 mg, 396 mg

Dunkin' Donuts Iced Coffee (Caramel Swirl) [s,m,l]: 278 mg, 267 mg, 357 mg

Dunkin' Donuts Iced Latte (6.92 mg/oz) [s,m,l]: 111 mg, 166 mg, 222 mg

Starbucks Doubleshot Energy: 135 mg

Starbucks = 25 mg/100 ml coffee (varies on coffee type)
1 Tablespoon of folgers classic roast = 71 mg
1 Teaspoon of folgers instant coffee = 74 mg
1 K-cup folgers classic roast = 100-150 mg
300 mg in 4.9 g of deathwish instant coffee

Half-Life

Caffeine has a long half-life (2-12 hours) that may vary depending on many factors, although the average half-life is 6.22 hours.
Nicotine (half-life 2 hours) can reduce the half-life of caffeine by ~50%, and alcohol consumption (50 g) can increase the half-life of caffeine by 72%. In women, the half-life is 10.5 hours during the last 4 weeks of pregnancy, 97.5 hours in a newborn, 14 hours in a 3-5 month old baby, and 2.6 hours in a baby older than 6 months. The half-life of caffeine in dogs is 6.66 hours, while in 1 day old puppies it is 47.5 hours.

Caffeine half-life while on nicotine is 3.5 hours https://pubmed.ncbi.nlm.nih.gov/657717/

Equivalence to other drugs:
5 mg of Ritalin is about 100 mg of Caffeine
600 mg of Caffeine is equal to a small dose of Amphetamine
Misc
Molar mass: 194.19 g/mol
Molecular formula: C8H10N4O2
Volume of distribution 0.7 L/kg
Clearance rate 0.078 L/kg/h
Half-life 6.22055 hours
Tmax 0.5 hours
Absorption half-life 4.7 minutes

alt tmax source: 29.8±8.1 minutes https://link.springer.com/article/10.1007/BF00613933

Caffeine tmax when ingested as liquid peaks in 1 hour (absorption half-life 12 minutes), when ingested as a pill its tmax is 30 minutes.