FAQ highlights: Not everyone responds
J Nutr 121:539546 Tamai I, Ohashi R, Nezu J, Yabuuchi H, Oku A, Shimane M, Sai Y, Tsuji A (1998) Molecular and functional identification of sodium ion-dependent, high affinity human carnitine transporter OCTN2

Other serious side effects that require medical attention include unexplainable muscle pain, muscle tenderness or weakness, dark brown urine (indicative of Rhabdomyolysis), increased levels of calcium (symptoms may include increased thirst, frequent urination, nausea, vomiting, constipation, pain in bones, confusion, and fatigue), high blood pressure (manifested as headache, dizziness, vision problems, and shortness of breath), palpitations, decreased blood platelet count (evidenced by bleeding or bruising, fatigue, and weakness), anemia symptoms such as fatigue, loss of energy, weakness, and shortness of breath, bronchitis symptoms like coughing and difficulty breathing, low blood sugar, seizures, and dermatitis exfoliative symptoms such as rashes, redness, widespread blistering, or peeling of the skin and mucosa (mouth)
Some patients progress through dose increases every 4 weeks
But this is a special case: drugs that are meant to be taken over the long term to address conditions that affect more than half of the US population
Neurological Manifestation Treatment Doses For those with B12 deficiency symptoms like nerve problems or brain fog, treatment needs to be stronger