Can he take vitamins after sahoor?

Allaah has
permitted those who fast to eat and drink until dawn comes. When dawn comes,
it is haraam to eat and drink, and it makes no difference whether what is
consumed is food or medicine. Allaah says (interpretation of the meaning): 

“and eat
and drink until the white thread (light) of dawn appears to you distinct
from the black thread (darkness of night)”

[al-Baqarah 2:187] 

It was
narrated from ‘Abd-Allaah ibn ‘Umar (may Allaah be pleased with him) that
the Messenger of Allaah (peace and blessings of Allaah be upon him)
said: “Bilaal gives the adhaan at night, so eat and drink until Ibn ‘Umm
Maktoom gives the call to prayer.” Then he – i.e., Ibn ‘Umar – said: He was
a blind man who did not give the call until it was said to him: “It is dawn,
it is dawn.” Narrated by al-Bukhaari (592), Muslim (1092).  

It was
narrated that Ibn Mas’ood (may Allaah be pleased with him) said: The
Messenger of Allaah (peace and blessings of Allaah be upon him) said:
“No one of you should let the adhaan of Bilaal prevent him from eating
sahoor. Rather he gives the call to prayer so that the one who is praying
qiyaam may rest and the one who is asleep may wake up.” Narrated by
al-Bukhaari (6802), Muslim (1093). 

Based on
this, it is permissible for you to take the medicine after sahoor if that is
before dawn breaks, and there is nothing wrong with that. The fact that the
effects of food and medicine remain in the body during the day in Ramadaan
is one of the blessings of sahoor. Hence it is prescribed to delay sahoor so
that the Muslim will have the strength to fast during the day in Ramadaan. 

We ask
Allaah to protect your spiritual and worldly affairs. 

And Allaah
knows best.