Effects of Low Doses of Caffeine on Mood, Physiology and Mental Function

Northumbria University

Status: Completed

Conditions: Healthy

Treatments: Drug: caffeine; Drug: Placebo

Study type: Interventional

Funder types: Other

Identifiers

NCT00487227

7G2CDCH

Details and patient eligibility

About

It is often assumed that levels of caffeine found in 'decaffeinated' beverages are below any psychopharmacological threshold. However, recent findings indicate that caffeine doses as low as 9 mg may be psychoactive. The effects of caffeine have also been shown up to 6 hours post-administration. The study aimed to establish the lowest active dose of caffeine, and to ascertain the duration of any effects.

Full description

The majority of recent caffeine studies have evaluated doses in the range of 75 - 150 mg or 1 - 2 mg/kg (approximately 130 - 260 ml fresh coffee). Such doses produce well characterised effects; including increased 'alertness', and improvements to measures of reaction time and sustained attention. A previous study has demonstrated improvements to performance following 9 mg caffeine, which represents the lowest known psychoactive dose of caffeine. A number of these effects, including elevated salivary caffeine levels, were still apparent at 6 hours post-caffeine consumption (9). Findings showing effects of 12.5 and 9 mg caffeine are important as these are approaching the levels found in decaffeinated beverages, which are assumed to have no behavioural or physiological effects. However, despite extensive research in this area, the lower threshold for psychoactive effects has not been established. A randomised, placebo-controlled, double-blind, balanced crossover study was undertaken. 20 young men and women (13 female, mean age 20.7 years, standard deviation 2.4) undertook computerised assessments of memory and attention and rated subjective mood. Autonomic activity and salivary caffeine were co-monitored. Assessment took place at baseline, 1, 3, 6, and 9 hours post-administration of placebo, 2.5, 5, and 10 mg caffeine (on separate days) administered in 150 ml fruit juice.

Enrollment: 20 patients

Sex: All

Ages: 18 to 35 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• native English speaker

Exclusion criteria

• pregnancy
• medication
• anaemia
• heart disorder
• diabetes
• respiratory disorder
• epilepsy
• asthma
• panic attacks
• habitual smoking
• food allergy

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Double Blind

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20 participants in 4 patient groups, including a placebo group

Placebo

Placebo Comparator group

Treatment:

Drug: Placebo

2.5mg caffeine

Experimental group

Treatment:

Drug: caffeine

5mg caffeine

Experimental group

Treatment:

Drug: caffeine

10mg caffeine

Experimental group

Treatment:

Drug: caffeine