Certain medications such as Metformin, H2-receptor antagonists including Zantac (Ranitidine), Tagamet(Cimetedine), Famotidine, Pepcid AC (Oral Pepcid), Axid AR (Nizatidine), Proton pump inhibitors (PPIs)including Prilosec (Omeprazole), Nexium (Esomeprazole), Prevacid (Lanzoprazole) and Antacids e.g:Gaviscon can also affect your ability to absorb vitamin B12
10.1677/erc.1.00973 54 FuJ.LiuS.HuM.LiaoX.WangX.XuZ.et al (2022)
A patient may first notice fewer bowel movements in the early weeks
Infection of the brain is common, followed by the kidneys, oral and nasal cavities, lymph nodes, lungs, spinal cord, and adrenal gland, and also reports of infection of heart, liver, stomach and bone
As for safety, tolerable upper intake levels (known as ULs) are set for vitamins and minerals when evidence is sufficient
That said, each individual is different and the amount of L-Carnitine received through diet differs, so please consult your healthcare practitioner for help in determining a safe and effective dose for your needs