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Caffeine

Evidence: ★★★★★ · Status: FDA Approved, OTC Supplement

💡 Did you know? Caffeine doesn't add energy. It blocks adenosine — the molecule that tells your brain you're tired — so the tiredness is just hidden, then arrives all at once.

In plain English

Adenosine is the "you're tired" molecule that builds up all day. Caffeine plugs into its parking spots so the tired signal can't land — you feel alert and exercise feels easier.

How it works

Competitive antagonist at adenosine A1 and A2A receptors (ADORA2A). Adenosine accumulates during wakefulness and signals fatigue; blocking it lifts the brakes on dopaminergic and cholinergic signalling, raises catecholamines, and lowers perceived exertion. Also mobilises free fatty acids, sparing glycogen.

Molecular target & official sources

ADORA2A adenosine A2A receptor (NCBI Gene) · Caffeine (PubChem CID 2519)

Protocol

3–6 mg/kg, 45–60 min pre-effort. Cycle off 10–14 days every ~2 months.

Watch out

5–6 h half-life (up to 9 h in slow metabolisers) — afternoon doses wreck deep sleep.

Bottom line

With creatine, one of the two most proven performance aids on earth.

Helps with: Build Muscle & Strength · Lose Fat · Endurance · Focus & Cognition

The human evidence

One of the most-replicated performance aids — meta-analyses show reliable small-to-moderate gains in endurance, power output and alertness. The alertness benefit is largest when you're sleep-deprived and much smaller at a well-rested baseline.

Stacks with

L-theanine (~200 mg) to smooth the jitters without dulling the focus.

Shares a pathway — often paired with: Semaglutide (Ozempic / Wegovy / Rybelsus), Tirzepatide (Mounjaro / Zepbound), Modafinil / Armodafinil, PDE-5 Inhibitors (Sildenafil / Tadalafil).

Avoid combining with

Other strong stimulants (yohimbine, high-dose synephrine) — additive heart-rate and blood-pressure load. Keep it >8–10 h from bedtime. Go easy if you’re prone to anxiety.

Availability & where to buy

Available over the counter. Widely available OTC — e.g. iHerb (ships worldwide); in Singapore also Guardian, Watsons, GNC, Shopee / Lazada. Look for a third-party-tested / GMP mark and check the dose per serving. Pennies — caffeine tablets are ~S$10–20 for months, or just coffee.

How it works: the GPCR → cAMP pathway →

Used in these protocols

Compare Caffeine

Common questions

Does Caffeine actually work?

Human-evidence rating: 5 of 5. With creatine, one of the two most proven performance aids on earth.

How do you take Caffeine?

3–6 mg/kg, 45–60 min pre-effort. Cycle off 10–14 days every ~2 months.

What are the risks or side effects of Caffeine?

5–6 h half-life (up to 9 h in slow metabolisers) — afternoon doses wreck deep sleep.

Is Caffeine legal or approved?

Regulatory status: FDA Approved, OTC Supplement.