Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| L-Carnitine (ALCAR / Acetyl-L-Carnitine) | L-Tyrosine | |
|---|---|---|
| Category | Amino Acids | Amino Acids |
| Standard Dose | 500-2000mg ALCAR daily or 1000-3000mg L-Carnitine L-Tartrate (for exercise performance) | 500-2000mg daily |
| Timing | Morning on empty stomach for cognitive effects. Pre-workout for fat oxidation/performance. ALCAR for brain; L-Carnitine L-Tartrate for muscle/exercise. | Morning on empty stomach (competes with other large neutral amino acids for BBB transport). 30-60 min before stressful tasks or exercise. |
| Cycle Duration | ongoing | As needed or cycle 4-8 weeks on, 2 weeks off |
| Evidence Level | strong_human | strong_human |
L-Carnitine's primary function is transporting long-chain fatty acids across the inner mitochondrial membrane via the carnitine shuttle (CPT-I/CPT-II system) for beta-oxidation. Acetyl-L-Carnitine (ALCAR) additionally donates its acetyl group to form acetyl-CoA (bypassing pyruvate dehydrogenase) and serves as a precursor for acetylcholine synthesis. ALCAR crosses the blood-brain barrier, providing neuroprotective effects through mitochondrial energetics, reduction of lipofuscin accumulation, enhancement of NGF receptor sensitivity, and modulation of synaptic plasticity. It also reduces oxidative stress via upregulation of heme oxygenase-1.
500-2000mg ALCAR daily or 1000-3000mg L-Carnitine L-Tartrate (for exercise performance)
Morning on empty stomach for cognitive effects. Pre-workout for fat oxidation/performance. ALCAR for brain; L-Carnitine L-Tartrate for muscle/exercise.
ongoing
L-Tyrosine is the precursor amino acid for catecholamine neurotransmitter synthesis: tyrosine hydroxylase converts tyrosine to L-DOPA (rate-limiting step), which is then converted to dopamine, norepinephrine, and epinephrine. It is also the precursor for thyroid hormones (iodination of tyrosine residues on thyroglobulin produces T3/T4) and melanin (via tyrosinase). Under conditions of acute stress, catecholamine turnover increases dramatically, depleting brain tyrosine pools. Supplementation provides substrate to maintain catecholamine synthesis during stress, sleep deprivation, cold exposure, and cognitive demand.
500-2000mg daily
Morning on empty stomach (competes with other large neutral amino acids for BBB transport). 30-60 min before stressful tasks or exercise.
As needed or cycle 4-8 weeks on, 2 weeks off
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