Stimulants & Caffeine

Overview

Caffeine is the world’s most widely consumed stimulant, found in coffee, tea, cocoa, energy drinks, and pre-workout supplements.
It acts on the central nervous system by blocking adenosine receptors, delaying fatigue and improving alertness.
While beneficial in moderate amounts, combining multiple stimulants (e.g., caffeine + guarana + yohimbine + theobromine) can lead to nervous and cardiovascular side effects.

Mechanism of action

Adenosine blockade → reduces the perception of fatigue.
Dopamine and adrenaline release → enhances vigilance, mood, and motivation.
Metabolic effect → stimulates lipolysis (fat oxidation).
Ergogenic effect → improves muscle contraction and reaction time.

What the evidence shows

Area	Evidence level	Observed effects
Alertness & focus	High	Reduces drowsiness, improves reaction time and attention.
Physical performance	High	Increases endurance and perceived energy (3–6 mg/kg).
Mood & motivation	Moderate	Slight short-term improvement in mood.
Sleep & anxiety	High (negative)	Delays sleep onset and increases nervousness depending on dose.

🔬 Overall level: High for alertness and performance.
Moderate for sustained cognitive enhancement (tolerance develops).

Benefits vs Risks

Moderate benefits	Excess risks
+ Energy and focus	– Insomnia, agitation
+ Sports performance	– Palpitations, tachycardia
+ Mood and vigilance	– Anxiety, nervousness
+ Metabolic stimulation	– Tremors, acid reflux
+ Enhanced fat oxidation	– Tolerance and dependency possible

💊 Dosage & forms

Use	Typical dose	Notes
General health (adult)	≤ 400 mg/day	Equivalent to 3–4 cups of coffee (Health Canada).
Pregnancy / breastfeeding	≤ 300 mg/day	Recommended limit by WHO and Health Canada.
Sports use	3–6 mg/kg	1 hour before exercise, do not exceed 400 mg.
Teenagers (13–18 years)	≤ 2.5 mg/kg/day	Individual tolerance varies.

☕ Equivalents:

Coffee 240 ml → ~95 mg
Espresso 30 ml → ~65 mg
Black tea 240 ml → ~50 mg
Energy drink 250 ml → 80–160 mg
Pre-workout → 100–400 mg, depending on brand

Tolerance & withdrawal

Tolerance: develops after 1–2 weeks of daily use.
Withdrawal: fatigue, headache, irritability within 12–24 h after stopping.
Best practice: cycle caffeine (e.g., 5 days on / 2 days off).
Hydration: important to prevent mild dehydration.

Synergies & balancing agents

Combination	Effect
Caffeine + L-Theanine	Calm focus: alertness without jitteriness.
Caffeine + Electrolytes	Sustained endurance and hydration.
Caffeine + Rhodiola / Ginseng	Possible adaptogenic synergy (watch dosing).
Caffeine + Ashwagandha	Balanced stimulation and relaxation (use cautiously).

⚠️ Risks & interactions

Consult a healthcare professional if you have cardiovascular disease, sleep disorders, anxiety, or are pregnant/breastfeeding.
Stacking stimulants in supplements (e.g., caffeine + guarana + yohimbine + theobromine) increases risk of serious side effects.
Common side effects: nervousness, tachycardia, insomnia, anxiety, tremors.
Withdrawal symptoms possible after chronic use (fatigue, headaches).
Possible interactions with medications: stimulants, antihypertensives, antidepressants, anxiolytics, anticoagulants.
Caffeine can potentiate or counteract certain drugs (e.g., analgesics, diuretics).

✅ Quality tips

Check total caffeine content on product labels.
Avoid stacked stimulant combinations (pre-workouts + energy drinks).
Do not consume after 4 p.m. to preserve sleep quality.
Stay hydrated (due to mild diuretic effect).
Prefer natural sources (coffee, green tea, yerba maté) over synthetic powders.

Sources

$- https://ods.od.nih.gov/factsheets/Caffeine-HealthProfessional/ - https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/caffeine.html - https://www.efsa.europa.eu/en/efsajournal/pub/4102 - https://examine.com/supplements/caffeine/

EFSA — Caffeine scientific opinion (2015)
NIH/ODS — Caffeine Health Factsheet
Health Canada — Dietary caffeine guidelines
Examine.com — Caffeine and performance meta-analyses