Since different jurists have different verdicts in this regard, you should act according to the fatwa (verdict) of the Mujtahid (jurist) whom you follow. For your information, we will now mention the verdicts of some of the religious authorities (jurists) as follows.
1) Some of the religious authorities[1] are of the view that anal intercourse is strongly abominable (makrooh).[2]
2) Some say[3]: “It is not permissible, as an obligatory precaution.”
3) Some others[4] are of the view that anal intercourse is not permissible, as an obligatory precaution, without wife’s consent. If she is consenting to it, it would be strongly abominable.[5]
For information about its physical harms and negative impacts, you should refer to medical science.
For further information in this regard refer to: Index: 601 (Sexual Pleasures and Their Limits).
[1] - Grand Ayatollahs including Imam Khomeini, Ayatollah Araki, Ayatollah Gulpaigani (may Allah bless them), Ayatollah Khamenei, Ayatollah Saafi, Ayatollah Makarem Shirazi and Ayatollah Zanjani.
[2] - See: Tahrir Al-Wasilah, vol.2, p. 241, Kitab al-Nikah, issue No. 11, Nejat al-‘Ibad (by Imam Khomeini), 35, Rules of Hayz, p.35
[3] - Grand Ayatollahs including Ayatollah Khoei, Ayatollah Tabrizi and Ayatollah Bahjat (may Allah bless them).
[4] - Grand Ayatollah Fazel Lankarani (may his soul rest in peace) and grand Ayatollah Sistani.
[5] - Tawzih al-Masail of Maraje’, vol.1, issue No. 450, Students’ Resalah, Sayyid Mujtaba Husseini, question 389, p. 243.