Table 2 Quality assessment of the randomized controlled clinical trials included

Veyna 2002 [6]

Monocenter

Not stated

Patients were blinded

Yes

2

van den Bergh 2005 [30]

Multicenter

Study medications were randomized and distributed by coordinating center

Principal investigators and assessors were blinded

Yes

4

Wong 2006 [9]

Monocenter

Sealed envelopes in order

Assessors and health care staff were blinded

Yes

4

Muroi 2008 [11]

Monocenter

Not stated

Patients were blinded

Yes

2

Westermaier 2010 [13]

Monocenter

Enveloped lot from a box

Assessors were blinded

Yes

4

Wong 2010 [12]

Multicenter

Randomization through Internet/sealed envelopes in order

Patients, assessors, and health care staff were blinded

Yes

4