Caffeine
Chapter 12
Lindsay Screws & Kaitlyn Dalecky
Caffeine
• Usually consumed for its stimulant effects
– (mice/rats ) low doses  stimulant effects; high doses reversed, reduced
activity
– (humans) low doses  stimulating and fatigue-reducing effects; high doses
 feelings of tension/anxiety
• Principal physcoactive ingredient in coffee
– Coffea arabica
• Most widely used drug worldwide
– 80-90% adults
– Average = 200-400 mg/day
Typical Caffeine Content of Common Food
Items and Drugs
Brewed coffee
Decaffeinated coffee
Tea
Regular/diet colas
Milk/sweet chocolate
Excedrin
No Doz
74-83 mg/5 oz. cup
2-3 mg/5 oz. cup
24-30 mg/5 oz. cup
26-58 mg/12 oz. serving
6-20 mg/oz.
64.8 mg/tablet
100mg/tablet
Caffeine: Pharmacology
• Theophylline
• Normally consumed p.o. (drank)
– Completely absorbed from the GI tract = 30-60 min
• Absorption begins in stomach but takes place mainly w/in the small intestine
• Half-life = varies from person to person
– Average = about 4 hours
• Converted to metabolites by the liver
– 95% eliminated through urine, 2-5% through feces, the rest through other
bodily fluids (saliva)
– 1-2% excreted unchanged
Theophylline
• Very similar actions of caffeine
• Three effects: bronchodilation, heart and CNS stimulation
• Antiasthmatic treatment
– Devoted to synthesizing safer asthma medicine
• Sleep apnea
• Can be taken p.o. or rectal and injectable form
Tolerance, Dependence, and Withdrawal
• High caffeine consumption  tolerance to cardiovascular and respiratory effects,
decreased noticeable effects
• Low caffeine consumption  little tolerance, more noticeable effects
Withdrawal Symptoms
• Symptoms can occur in individuals who consume as little as 100 mg/day
– symptoms = headache, lethargy or fatigue
– Means dependency
• Lasts for a few days, then dissipate
– Begins at 18th hr of abstinence
• Positive correlation between strength of dependency and severity of withdrawal
symptoms
Side Effects
• Little evidence to link w/ serious disease
• Possibly raises cholesterol levels & BP
• Directly related to fibrocystic breast disease
– Can go away w/ the absence of usage
• Heartburn
• Interaction with alcohol
– Just as drunk, but more aroused
• Not recommended for pregnant women, light sleepers, very young/old, and
cardiac patients
Mechanisms of Action
• Does not directly influence catecholamine systems
• Blocks GABAA –R, stimulates Ca2+ w/in cells  high/toxic doses
• Blocks A1 and A2A –R (adenosine)  low doses
• Adenosine = part of ATP (energy)
– In brain, also acts as a NT
– One explanation why first cup of coffee in the morning wakes some people
up; refreshes a worker after post-lunch drowsiness; keeps a non-tolerant
individual up at night if consumes late-night coffee
Caffeine Abuse
• Caffeinism
– Restlessness, nervousness, insomnia, physiological disturbances (tachycardia)
• Difficult to distinguish from anxiety disorder
– Individuals may experience strong withdrawal symptoms and cravings if
attempt to stop usage
• Has characteristics of an abused substance but usually not compulsive and doesn’t
affect daily function
– RFT of caffeine not due to drug=induced euphoria like those of other abused
drugs