Acetyl L-carnitine (ALCAR) has some scientific evidence supporting its effects on the nervous system, including potential benefits related to the sympathetic nervous system, though the evidence is moderate and not definitive. ALCAR is an acetylated form of L-carnitine that crosses the blood-brain barrier and is involved in mitochondrial energy metabolism. Some studies suggest that ALCAR may enhance neuronal energy production and support neurotransmitter synthesis, which could modulate sympathetic nervous system activity. For example, research has indicated ALCAR may increase levels of norepinephrine and dopamine in the central nervous system, which are key neurotransmitters involved in sympathetic nervous system responses (Virmani et al., 2003). Additionally, some animal and limited human studies have shown that ALCAR supplementation can improve autonomic function, including heart rate variability and nerve conduction, possibly reflecting support of sympathetic and parasympathetic balance (Jones et al., 2007).

However, most clinical research on ALCAR has focused on its use in cognitive decline, neuropathy, and mood disorders rather than direct support of the sympathetic nervous system. The available evidence suggests a plausible mechanism, but more targeted clinical trials are needed to establish a clear benefit specifically for sympathetic nervous system support. Thus, while there is some scientific basis, the evidence is not robust enough to warrant a higher rating.