These include cellular metabolism, DNA synthesis, fatty acid and amino acid metabolism, and red blood cell formation
For a detailed breakdown of this pathway, see 5-Amino-1MQ for Beginners: Dosage, Benefits, and Peptide Stacks Explained
For patients who do not respond to two or more antidepressant trials, advanced options like TMS or Spravato (esketamine, FDA-approved for treatment-resistant depression in 2019) can help (FDA News Release, March 2019)

B12 has many functions in our body, so unfortunately a deficiency will give rise to a wide variety of symptoms, like brain fog, memory problems, cognitive impairment, insomnia, headaches, especially migraine, behavioural changes, learning problems, nominal aphasia, mood swings, irritability, depression, anxiety, hallucinations, delusions, psychosis, peripheral paraesthesia (pins and needles), numbness, neuropathic pains, poor balance, reduced vibration sense or proprioception (joint position sense), tinnitus, ataxia, taste impairment, sometimes myelopathy, fatigue, anaemia (either with larger red blood cells, or with normal size of the red blood cells when there is also iron deficiency), other reduction in blood cells, abdominal complaints, malabsorption, failure to thrive, weight loss, diarrhoea, hyperpigmentation, glossitis, (aphthous) stomatitis, infertility, urinary tract infections, joint and muscle pain, muscle weakness, spasticity, seizures, cardiomyopathy, urinary and/or faecal incontinence, postural hypotension/dizziness, erectile dysfunction, to name a few
