Form of Vitamin B12: The type of vitamin B12 used also plays a role
Understanding this two-phase timeline helps explain why some patients experience symptoms very quickly after starting tirzepatide, while others notice gradual changes over several months as their weight drops
By contrast, phentermine is taken daily as an oral medication, usually in a dosage of 37.5mg, but there is a lower dosage of 15mg for those with health concerns such as renal impairment, which is when your kidney doesnt function correctly
This makes scheduling simple
Scientific References EBioMedicine, 2024 GLP-1 receptors in brain reward circuits and desire Kinsey Institute, 2025 Survey of 2,000 adults on GLP-1 sexual desire effects International Journal of Impotence Research, 2025 FDA adverse events GLP-1 sexual dysfunction Journal of Sexual Medicine, 2025 Serotonin 5-HT2C pathway and libido on GLP-1s