According to the Game Database of ChessTempo, 7....Qb6 is actually more popular than 7....h6.
At the very top level, both moves have their supporters, e.g. Anand and Grischuk for 7....Qb6 and Vachier-Lagrave and Nepomniachtchi for 7....h6.
Both moves can easily transpose, as the main line of the Poisoned Pawn goes 7....Qb6 8.Qd2 Qxb2 9.Rb1 Qa3 10.e5 h6 11.Bh4.
After 7....Qb6, white has the option to play 8.Nb3, as mentioned by Seth-Riley. With the inclusion of 7....h6 8.Bh4, 9.Nb3 is not possible because of 9....Qe3+.
However, after 7....h6 8.Bh4 Qb6, white has the option to play 9.a3. If black takes the pawn with 9....Qxb2, white can trap the queen by 10.Na4. Instead black should continue his development, for instance with 9....Be7. Now white can play 10.Bf2, which is of course possible thanks to the inclusion of 7....h6 8.Bh4.
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5 e6 7.f4 h6 (7...Qb6 8.Qd2 (8.Nb3) Qxb2 9.Rb1 Qa3 10.e5 h6 11.Bh4) 8.Bh4 Qb6 9.a3 (9.Nb3 Qe3+)(9.Qd2 Qxb2 10.Rb1 Qa3 11.e5) Be7 (9...Qxb2 10.Na4) 10.Bf2