CaffeineChapter 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 74-83 mg/5 oz. cupDecaffeinated coffee 2-3 mg/5 oz. cupTea 24-30 mg/5 oz. cupRegular/diet colas 26-58 mg/12 oz.

servingMilk/sweet chocolate 6-20 mg/oz.Excedrin 64.8 mg/tabletNo Doz 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