Is it permissible to have an injection to stop menses for a number of hours in order to do tawaaf?

There is nothing wrong with it in cases of necessity, but
that is on condition that this should be with the consent of a doctor. If
the doctor says that there is nothing wrong with having this injection or
taking these pills, then there is nothing wrong with it in a case of
necessity, whether it is for a number of hours or a number of days. End
quote. 

Majmoo’ Fataawa Ibn ‘Uthaymeen,
22/392 

The Shaykh was also asked about a woman whose period came
during tawaaf al-ifaadah. She told the female doctor who was with the group
about that, and the doctor said: I will give you an injection that will stop
the bleeding for six hours. And in fact the bleeding stopped for six hours,
so she did tawaaf again and did saa’i. And after six hours her period came
back. It is what she did valid or what? 

He replied: If the bleeding stopped completely and she was
pure — and women know what the tuhr (sign of purity) is, then there is
nothing wrong with it and her tawaaf is valid. But if it was not a real
tuhr, then she did tawaaf before she became pure, and if a woman does tawaaf
before she becomes pure, it is not valid. End quote. 

Majmoo’ Fataawa Ibn ‘Uthaymeen,
22/393, 394 

For more information please see the answer to questions number 20467 and 36600.